diff --git a/builtin/game/item_entity.lua b/builtin/game/item_entity.lua
index 20dd18044..b5bce81f0 100644
--- a/builtin/game/item_entity.lua
+++ b/builtin/game/item_entity.lua
@@ -195,8 +195,12 @@ core.register_entity(":__builtin:item", {
 			return -- Don't do anything
 		end
 
-		assert(moveresult,
-			"Collision info missing, this is caused by an out-of-date/buggy mod or game")
+		-- assert(moveresult,
+		-- 	"Collision info missing, this is caused by an out-of-date/buggy mod or game")
+		if not moveresult then
+			self.object:set_velocity({x=0, y=0, z=0})
+			return
+		end
 
 		if not moveresult.collides then
 			-- future TODO: items should probably decelerate in air
diff --git a/builtin/game/models/mc_compat_character.b3d b/builtin/game/models/mc_compat_character.b3d
new file mode 100644
index 000000000..8147edc6d
Binary files /dev/null and b/builtin/game/models/mc_compat_character.b3d differ
diff --git a/src/activeobject.h b/src/activeobject.h
index d97014c96..24576f358 100644
--- a/src/activeobject.h
+++ b/src/activeobject.h
@@ -44,15 +44,18 @@ enum ActiveObjectType {
 
 struct ActiveObjectMessage
 {
-	ActiveObjectMessage(u16 id_, bool reliable_=true, const std::string &data_ = "") :
+	ActiveObjectMessage(u16 id_, bool reliable_ = true,
+			const std::string &data_ = "", const std::string legacy_ = "") :
 		id(id_),
 		reliable(reliable_),
-		datastring(data_)
+		datastring(data_),
+		legacystring(legacy_)
 	{}
 
 	u16 id;
 	bool reliable;
 	std::string datastring;
+	std::string legacystring;
 };
 
 enum ActiveObjectCommand {
diff --git a/src/clientiface.cpp b/src/clientiface.cpp
index e08df78f3..adf039232 100644
--- a/src/clientiface.cpp
+++ b/src/clientiface.cpp
@@ -750,8 +750,8 @@ void ClientInterface::sendToAllCompat(NetworkPacket *pkt, NetworkPacket *legacyp
 		} else if (client->net_proto_version != 0) {
 			pkt_to_send = legacypkt;
 		} else {
-			warningstream << "Client with unhandled version to handle: '"
-				<< client->net_proto_version << "'";
+			// This will happen if a client is connecting when sendToAllCompat
+			// is called, this can safely be ignored.
 			continue;
 		}
 
@@ -762,6 +762,34 @@ void ClientInterface::sendToAllCompat(NetworkPacket *pkt, NetworkPacket *legacyp
 	}
 }
 
+void ClientInterface::oldSendToAll(NetworkPacket *pkt)
+{
+	RecursiveMutexAutoLock clientslock(m_clients_mutex);
+	for (auto &client_it : m_clients) {
+		RemoteClient *client = client_it.second;
+
+		if (client->net_proto_version != 0 && client->net_proto_version < 37) {
+			m_con->Send(client->peer_id,
+				clientCommandFactoryTable[pkt->getCommand()].channel, pkt,
+				clientCommandFactoryTable[pkt->getCommand()].reliable);
+			}
+	}
+}
+
+void ClientInterface::newSendToAll(NetworkPacket *pkt)
+{
+	RecursiveMutexAutoLock clientslock(m_clients_mutex);
+	for (auto &client_it : m_clients) {
+		RemoteClient *client = client_it.second;
+
+		if (client->net_proto_version > 36) {
+			m_con->Send(client->peer_id,
+				clientCommandFactoryTable[pkt->getCommand()].channel, pkt,
+				clientCommandFactoryTable[pkt->getCommand()].reliable);
+			}
+	}
+}
+
 RemoteClient* ClientInterface::getClientNoEx(session_t peer_id, ClientState state_min)
 {
 	RecursiveMutexAutoLock clientslock(m_clients_mutex);
diff --git a/src/clientiface.h b/src/clientiface.h
index 3b272b26f..09897819b 100644
--- a/src/clientiface.h
+++ b/src/clientiface.h
@@ -458,6 +458,8 @@ public:
 	/* send to all clients */
 	void sendToAll(NetworkPacket *pkt);
 	void sendToAllCompat(NetworkPacket *pkt, NetworkPacket *legacypkt, u16 min_proto_ver);
+	void oldSendToAll(NetworkPacket *pkt);
+	void newSendToAll(NetworkPacket *pkt);
 
 	/* delete a client */
 	void DeleteClient(session_t peer_id);
diff --git a/src/itemdef.cpp b/src/itemdef.cpp
index 2f0badbe1..638bf0a45 100644
--- a/src/itemdef.cpp
+++ b/src/itemdef.cpp
@@ -126,6 +126,11 @@ void ItemDefinition::serialize(std::ostream &os, u16 protocol_version) const
 {
 	// protocol_version >= 37
 	u8 version = 6;
+
+	// protocol_version < 37
+	if (protocol_version < 37)
+		version = 3;
+
 	writeU8(os, version);
 	writeU8(os, type);
 	os << serializeString(name);
@@ -153,13 +158,25 @@ void ItemDefinition::serialize(std::ostream &os, u16 protocol_version) const
 
 	os << serializeString(node_placement_prediction);
 
-	// Version from ContentFeatures::serialize to keep in sync
-	sound_place.serialize(os, CONTENTFEATURES_VERSION);
-	sound_place_failed.serialize(os, CONTENTFEATURES_VERSION);
+	if (version == 3) {
+		os << serializeString(sound_place.name);
+		writeF1000(os, sound_place.gain);
+		writeF1000(os, range);
+		os << serializeString(sound_place_failed.name);
+		writeF1000(os, sound_place_failed.gain);
+	} else {
+		// Version from ContentFeatures::serialize to keep in sync
+		sound_place.serialize(os, CONTENTFEATURES_VERSION);
+		sound_place_failed.serialize(os, CONTENTFEATURES_VERSION);
+		writeF32(os, range);
+	}
 
-	writeF(os, range, protocol_version);
 	os << serializeString(palette_image);
 	writeARGB8(os, color);
+
+	if (version == 3)
+		return;
+
 	os << serializeString(inventory_overlay);
 	os << serializeString(wield_overlay);
 }
diff --git a/src/mapblock.cpp b/src/mapblock.cpp
index 3b6f7a138..f0b6f4e77 100644
--- a/src/mapblock.cpp
+++ b/src/mapblock.cpp
@@ -355,7 +355,7 @@ static void correctBlockNodeIds(const NameIdMapping *nimap, MapNode *nodes,
 	}
 }
 
-void MapBlock::serialize(std::ostream &os, u8 version, bool disk)
+void MapBlock::serialize(std::ostream &os, u8 version, bool disk, std::string formspec_prepend)
 {
 	if(!ser_ver_supported(version))
 		throw VersionMismatchException("ERROR: MapBlock format not supported");
@@ -411,7 +411,7 @@ void MapBlock::serialize(std::ostream &os, u8 version, bool disk)
 		Node metadata
 	*/
 	std::ostringstream oss(std::ios_base::binary);
-	m_node_metadata.serialize(oss, version, disk);
+	m_node_metadata.serialize(oss, version, disk, false, formspec_prepend);
 	compressZlib(oss.str(), os);
 
 	/*
diff --git a/src/mapblock.h b/src/mapblock.h
index ea05f85a3..b5272a31e 100644
--- a/src/mapblock.h
+++ b/src/mapblock.h
@@ -482,7 +482,8 @@ public:
 	// These don't write or read version by itself
 	// Set disk to true for on-disk format, false for over-the-network format
 	// Precondition: version >= SER_FMT_VER_LOWEST_WRITE
-	void serialize(std::ostream &os, u8 version, bool disk);
+	void serialize(std::ostream &os, u8 version, bool disk,
+		std::string formspec_prepend="");
 	// If disk == true: In addition to doing other things, will add
 	// unknown blocks from id-name mapping to wndef
 	void deSerialize(std::istream &is, u8 version, bool disk);
diff --git a/src/network/networkpacket.h b/src/network/networkpacket.h
index 19c06113b..3e87809b4 100644
--- a/src/network/networkpacket.h
+++ b/src/network/networkpacket.h
@@ -44,6 +44,7 @@ public:
 	u16 getCommand() { return m_command; }
 	const u32 getRemainingBytes() const { return m_datasize - m_read_offset; }
 	const char *getRemainingString() { return getString(m_read_offset); }
+	u16 getProtocolVersion() const { return m_protocol_version; }
 
 	// Returns a c-string without copying.
 	// A better name for this would be getRawString()
diff --git a/src/network/networkprotocol.h b/src/network/networkprotocol.h
index f4c39a992..2368e3c7c 100644
--- a/src/network/networkprotocol.h
+++ b/src/network/networkprotocol.h
@@ -210,7 +210,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #define LATEST_PROTOCOL_VERSION_STRING TOSTRING(LATEST_PROTOCOL_VERSION)
 
 // Server's supported network protocol range
-#define SERVER_PROTOCOL_VERSION_MIN 37
+#define SERVER_PROTOCOL_VERSION_MIN 25
 #define SERVER_PROTOCOL_VERSION_MAX LATEST_PROTOCOL_VERSION
 
 // Client's supported network protocol range
diff --git a/src/network/serveropcodes.cpp b/src/network/serveropcodes.cpp
index 91e9c54c0..06620d6f4 100644
--- a/src/network/serveropcodes.cpp
+++ b/src/network/serveropcodes.cpp
@@ -89,7 +89,7 @@ const ToServerCommandHandler toServerCommandTable[TOSERVER_NUM_MSG_TYPES] =
 	null_command_handler, // 0x3e
 	null_command_handler, // 0x3f
 	{ "TOSERVER_REQUEST_MEDIA",            TOSERVER_STATE_STARTUP, &Server::handleCommand_RequestMedia }, // 0x40
-	null_command_handler, // 0x41
+ 	{ "TOSERVER_RECEIVED_MEDIA",           TOSERVER_STATE_STARTUP, &Server::handleCommand_Deprecated }, // 0x41 not used by the server since protocol version 23
 	null_command_handler, // 0x42
 	{ "TOSERVER_CLIENT_READY",             TOSERVER_STATE_STARTUP, &Server::handleCommand_ClientReady }, // 0x43
 	null_command_handler, // 0x44
diff --git a/src/network/serverpackethandler.cpp b/src/network/serverpackethandler.cpp
index 5a58cbd51..06f253958 100644
--- a/src/network/serverpackethandler.cpp
+++ b/src/network/serverpackethandler.cpp
@@ -324,7 +324,7 @@ void Server::handleCommand_Init2(NetworkPacket* pkt)
 	sendDetachedInventories(peer_id, false);
 
 	// Send player movement settings
-	SendMovement(peer_id);
+	SendMovement(peer_id, protocol_version);
 
 	// Send time of day
 	u16 time = m_env->getTimeOfDay();
@@ -454,7 +454,7 @@ void Server::handleCommand_GotBlocks(NetworkPacket* pkt)
 void Server::process_PlayerPos(RemotePlayer *player, PlayerSAO *playersao,
 	NetworkPacket *pkt)
 {
-	if (pkt->getRemainingBytes() < 12 + 12 + 4 + 4 + 4 + 1 + 1)
+	if (pkt->getRemainingBytes() < 12 + 12 + 4 + 4)
 		return;
 
 	v3s32 ps, ss;
@@ -474,10 +474,14 @@ void Server::process_PlayerPos(RemotePlayer *player, PlayerSAO *playersao,
 	f32 fov = 0;
 	u8 wanted_range = 0;
 
-	*pkt >> keyPressed;
-	*pkt >> f32fov;
-	fov = (f32)f32fov / 80.0f;
-	*pkt >> wanted_range;
+	if (pkt->getRemainingBytes() >= 4)
+		*pkt >> keyPressed;
+	if (pkt->getRemainingBytes() >= 1) {
+		*pkt >> f32fov;
+		fov = (f32)f32fov / 80.0f;
+		if (pkt->getRemainingBytes() >= 1)
+			*pkt >> wanted_range;
+	}
 
 	v3f position((f32)ps.X / 100.0f, (f32)ps.Y / 100.0f, (f32)ps.Z / 100.0f);
 	v3f speed((f32)ss.X / 100.0f, (f32)ss.Y / 100.0f, (f32)ss.Z / 100.0f);
@@ -791,9 +795,6 @@ void Server::handleCommand_ChatMessage(NetworkPacket* pkt)
 
 void Server::handleCommand_Damage(NetworkPacket* pkt)
 {
-	u16 damage;
-
-	*pkt >> damage;
 
 	session_t peer_id = pkt->getPeerId();
 	RemotePlayer *player = m_env->getPlayer(peer_id);
@@ -806,6 +807,17 @@ void Server::handleCommand_Damage(NetworkPacket* pkt)
 		return;
 	}
 
+	u16 damage;
+
+	// Minetest 0.4 uses 8-bit integers for damage.
+	if (player->protocol_version >= 37) {
+		*pkt >> damage;
+	} else {
+		u8 raw_damage;
+		*pkt >> raw_damage;
+		damage = raw_damage;
+	}
+
 	PlayerSAO *playersao = player->getPlayerSAO();
 	if (playersao == NULL) {
 		errorstream <<
@@ -1670,7 +1682,7 @@ void Server::handleCommand_SrpBytesM(NetworkPacket* pkt)
 	if (client->chosen_mech != AUTH_MECHANISM_SRP &&
 			client->chosen_mech != AUTH_MECHANISM_LEGACY_PASSWORD) {
 		actionstream << "Server: got SRP _M packet, while auth"
-			<< "is going on with mech " << client->chosen_mech << " from " 
+			<< "is going on with mech " << client->chosen_mech << " from "
 			<< addr_s << " (wantSudo=" << wantSudo << "). Denying." << std::endl;
 		if (wantSudo) {
 			DenySudoAccess(peer_id);
diff --git a/src/nodedef.cpp b/src/nodedef.cpp
index 80a2d5388..4acdc5508 100644
--- a/src/nodedef.cpp
+++ b/src/nodedef.cpp
@@ -74,7 +74,13 @@ void NodeBox::reset()
 void NodeBox::serialize(std::ostream &os, u16 protocol_version) const
 {
 	// Protocol >= 36
-	const u8 version = 6;
+	u8 version;
+	if (protocol_version >= 36)
+		version = 6;
+	else if (protocol_version >= 27)
+		version = 3;
+	else
+		version = 2;
 	writeU8(os, version);
 
 	switch (type) {
@@ -84,28 +90,38 @@ void NodeBox::serialize(std::ostream &os, u16 protocol_version) const
 
 		writeU16(os, fixed.size());
 		for (const aabb3f &nodebox : fixed) {
-			writeV3F32(os, nodebox.MinEdge);
-			writeV3F32(os, nodebox.MaxEdge);
+			writeV3F(os, nodebox.MinEdge, protocol_version);
+			writeV3F(os, nodebox.MaxEdge, protocol_version);
 		}
 		break;
 	case NODEBOX_WALLMOUNTED:
 		writeU8(os, type);
 
-		writeV3F32(os, wall_top.MinEdge);
-		writeV3F32(os, wall_top.MaxEdge);
-		writeV3F32(os, wall_bottom.MinEdge);
-		writeV3F32(os, wall_bottom.MaxEdge);
-		writeV3F32(os, wall_side.MinEdge);
-		writeV3F32(os, wall_side.MaxEdge);
+		writeV3F(os, wall_top.MinEdge, protocol_version);
+		writeV3F(os, wall_top.MaxEdge, protocol_version);
+		writeV3F(os, wall_bottom.MinEdge, protocol_version);
+		writeV3F(os, wall_bottom.MaxEdge, protocol_version);
+		writeV3F(os, wall_side.MinEdge, protocol_version);
+		writeV3F(os, wall_side.MaxEdge, protocol_version);
 		break;
 	case NODEBOX_CONNECTED:
+		if (version <= 2) {
+			// send old clients nodes that can't be walked through
+			// to prevent abuse
+			writeU8(os, NODEBOX_FIXED);
+
+			writeU16(os, 1);
+			writeV3F1000(os, v3f(-BS/2, -BS/2, -BS/2));
+			writeV3F1000(os, v3f(BS/2, BS/2, BS/2));
+			break;
+		}
 		writeU8(os, type);
 
 #define WRITEBOX(box) \
 		writeU16(os, (box).size()); \
 		for (const aabb3f &i: (box)) { \
-			writeV3F32(os, i.MinEdge); \
-			writeV3F32(os, i.MaxEdge); \
+			writeV3F(os, i.MinEdge, protocol_version); \
+			writeV3F(os, i.MaxEdge, protocol_version); \
 		};
 
 		WRITEBOX(fixed);
@@ -115,14 +131,17 @@ void NodeBox::serialize(std::ostream &os, u16 protocol_version) const
 		WRITEBOX(connect_left);
 		WRITEBOX(connect_back);
 		WRITEBOX(connect_right);
-		WRITEBOX(disconnected_top);
-		WRITEBOX(disconnected_bottom);
-		WRITEBOX(disconnected_front);
-		WRITEBOX(disconnected_left);
-		WRITEBOX(disconnected_back);
-		WRITEBOX(disconnected_right);
-		WRITEBOX(disconnected);
-		WRITEBOX(disconnected_sides);
+
+		if (version > 5) {
+			WRITEBOX(disconnected_top);
+			WRITEBOX(disconnected_bottom);
+			WRITEBOX(disconnected_front);
+			WRITEBOX(disconnected_left);
+			WRITEBOX(disconnected_back);
+			WRITEBOX(disconnected_right);
+			WRITEBOX(disconnected);
+			WRITEBOX(disconnected_sides);
+		}
 		break;
 	default:
 		writeU8(os, type);
@@ -207,12 +226,41 @@ void NodeBox::deSerialize(std::istream &is)
 
 void TileDef::serialize(std::ostream &os, u16 protocol_version) const
 {
-	// protocol_version >= 36
-	u8 version = 6;
+	u8 version;
+	if (protocol_version >= 37)
+		version = 6;
+	else if (protocol_version >= 30)
+		version = 4;
+	else if (protocol_version >= 29)
+		version = 3;
+	else if (protocol_version >= 26)
+		version = 2;
+	else
+		version = 1;
+
 	writeU8(os, version);
 
 	os << serializeString(name);
 	animation.serialize(os, version);
+
+	// Compatibility with Minetest 0.4.
+	if (version < 6) {
+		writeU8(os, backface_culling);
+		if (version < 2)
+			return;
+		writeU8(os, tileable_horizontal);
+		writeU8(os, tileable_vertical);
+		if (version < 3)
+		 	return;
+		writeU8(os, has_color);
+		if (has_color) {
+			writeU8(os, color.getRed());
+			writeU8(os, color.getGreen());
+			writeU8(os, color.getBlue());
+		}
+		return;
+	}
+
 	bool has_scale = scale > 0;
 	u16 flags = 0;
 	if (backface_culling)
@@ -424,7 +472,14 @@ void ContentFeatures::reset()
 
 void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 {
-	const u8 version = CONTENTFEATURES_VERSION;
+	if (protocol_version < 31) {
+		serializeOld(os, protocol_version);
+		return;
+	}
+
+	u8 version = CONTENTFEATURES_VERSION;
+	if (protocol_version < 37)
+		version = 10;
 	writeU8(os, version);
 
 	// general
@@ -440,7 +495,7 @@ void ContentFeatures::serialize(std::ostream &os, u16 protocol_version) const
 	// visual
 	writeU8(os, drawtype);
 	os << serializeString(mesh);
-	writeF32(os, visual_scale);
+	writeF(os, visual_scale, protocol_version);
 	writeU8(os, 6);
 	for (const TileDef &td : tiledef)
 		td.serialize(os, protocol_version);
@@ -1125,6 +1180,105 @@ void ContentFeatures::updateTextures(ITextureSource *tsrc, IShaderSource *shdsrc
 }
 #endif
 
+//// Serialization of old ContentFeatures formats
+void ContentFeatures::serializeOld(std::ostream &os, u16 protocol_version) const
+{
+	u8 compatible_param_type_2 = param_type_2;
+	if ((protocol_version < 28)
+			&& (compatible_param_type_2 == CPT2_MESHOPTIONS))
+		compatible_param_type_2 = CPT2_NONE;
+	else if (protocol_version < 30) {
+		if (compatible_param_type_2 == CPT2_COLOR)
+			compatible_param_type_2 = CPT2_NONE;
+		else if (compatible_param_type_2 == CPT2_COLORED_FACEDIR)
+			compatible_param_type_2 = CPT2_FACEDIR;
+		else if (compatible_param_type_2 == CPT2_COLORED_WALLMOUNTED)
+			compatible_param_type_2 = CPT2_WALLMOUNTED;
+	}
+
+	float compatible_visual_scale = visual_scale;
+	if (protocol_version < 30 && drawtype == NDT_PLANTLIKE)
+		compatible_visual_scale = sqrt(visual_scale);
+
+	TileDef compatible_tiles[6];
+	for (u8 i = 0; i < 6; i++) {
+		compatible_tiles[i] = tiledef[i];
+		if (tiledef_overlay[i].name != "") {
+			std::stringstream s;
+			s << "(" << tiledef[i].name << ")^(" << tiledef_overlay[i].name
+				<< ")";
+			compatible_tiles[i].name = s.str();
+		}
+	}
+
+	// Protocol >= 24
+	if (protocol_version < 31) {
+		const u8 version = protocol_version < 27 ? 7 : 8;
+		writeU8(os, version);
+
+		os << serializeString(name);
+		writeU16(os, groups.size());
+		for (ItemGroupList::const_iterator i = groups.begin();
+				i != groups.end(); ++i) {
+			os << serializeString(i->first);
+			writeS16(os, i->second);
+		}
+		writeU8(os, drawtype);
+		writeF1000(os, compatible_visual_scale);
+		writeU8(os, 6);
+		for (u32 i = 0; i < 6; i++)
+			compatible_tiles[i].serialize(os, protocol_version);
+		writeU8(os, CF_SPECIAL_COUNT);
+		for (u32 i = 0; i < CF_SPECIAL_COUNT; i++)
+			tiledef_special[i].serialize(os, protocol_version);
+		writeU8(os, alpha);
+		writeU8(os, post_effect_color.getAlpha());
+		writeU8(os, post_effect_color.getRed());
+		writeU8(os, post_effect_color.getGreen());
+		writeU8(os, post_effect_color.getBlue());
+		writeU8(os, param_type);
+		writeU8(os, compatible_param_type_2);
+		writeU8(os, is_ground_content);
+		writeU8(os, light_propagates);
+		writeU8(os, sunlight_propagates);
+		writeU8(os, walkable);
+		writeU8(os, pointable);
+		writeU8(os, diggable);
+		writeU8(os, climbable);
+		writeU8(os, buildable_to);
+		os << serializeString(""); // legacy: used to be metadata_name
+		writeU8(os, liquid_type);
+		os << serializeString(liquid_alternative_flowing);
+		os << serializeString(liquid_alternative_source);
+		writeU8(os, liquid_viscosity);
+		writeU8(os, liquid_renewable);
+		writeU8(os, light_source);
+		writeU32(os, damage_per_second);
+		node_box.serialize(os, protocol_version);
+		selection_box.serialize(os, protocol_version);
+		writeU8(os, legacy_facedir_simple);
+		writeU8(os, legacy_wallmounted);
+		sound_footstep.serialize(os, version);
+		sound_dig.serialize(os, version);
+		sound_dug.serialize(os, version);
+		writeU8(os, rightclickable);
+		writeU8(os, drowning);
+		writeU8(os, leveled);
+		writeU8(os, liquid_range);
+		writeU8(os, waving);
+		os << serializeString(mesh);
+		collision_box.serialize(os, protocol_version);
+		writeU8(os, floodable);
+		writeU16(os, connects_to_ids.size());
+		for (u16 connects_to_id : connects_to_ids)
+			writeU16(os, connects_to_id);
+		writeU8(os, connect_sides);
+	} else {
+		throw SerializationError("ContentFeatures::serialize(): "
+			"Unsupported version requested");
+	}
+}
+
 /*
 	NodeDefManager
 */
diff --git a/src/nodedef.h b/src/nodedef.h
index 525f6e4d3..711e8443a 100644
--- a/src/nodedef.h
+++ b/src/nodedef.h
@@ -414,6 +414,7 @@ struct ContentFeatures
 	void serialize(std::ostream &os, u16 protocol_version) const;
 	void deSerialize(std::istream &is);
 	void deSerializeOld(std::istream &is, int version);
+	void serializeOld(std::ostream &os, u16 protocol_version) const;
 	/*!
 	 * Since vertex alpha is no longer supported, this method
 	 * adds opacity directly to the texture pixels.
diff --git a/src/nodemetadata.cpp b/src/nodemetadata.cpp
index 801aa47fa..ef498c5a5 100644
--- a/src/nodemetadata.cpp
+++ b/src/nodemetadata.cpp
@@ -40,7 +40,8 @@ NodeMetadata::~NodeMetadata()
 	delete m_inventory;
 }
 
-void NodeMetadata::serialize(std::ostream &os, u8 version, bool disk) const
+void NodeMetadata::serialize(std::ostream &os, u8 version, bool disk,
+		std::string formspec_prepend) const
 {
 	int num_vars = disk ? m_stringvars.size() : countNonPrivate();
 	writeU32(os, num_vars);
@@ -50,7 +51,11 @@ void NodeMetadata::serialize(std::ostream &os, u8 version, bool disk) const
 			continue;
 
 		os << serializeString(sv.first);
-		os << serializeLongString(sv.second);
+		if (!formspec_prepend.empty() && sv.first == "formspec" &&
+				sv.second.find("no_prepend[]") == std::string::npos)
+			os << serializeLongString(sv.second + formspec_prepend);
+		else
+			os << serializeLongString(sv.second);
 		if (version >= 2)
 			writeU8(os, (priv) ? 1 : 0);
 	}
@@ -113,7 +118,7 @@ int NodeMetadata::countNonPrivate() const
 */
 
 void NodeMetadataList::serialize(std::ostream &os, u8 blockver, bool disk,
-	bool absolute_pos) const
+	bool absolute_pos, std::string formspec_prepend) const
 {
 	/*
 		Version 0 is a placeholder for "nothing to see here; go away."
@@ -146,7 +151,7 @@ void NodeMetadataList::serialize(std::ostream &os, u8 blockver, bool disk,
 			u16 p16 = (p.Z * MAP_BLOCKSIZE + p.Y) * MAP_BLOCKSIZE + p.X;
 			writeU16(os, p16);
 		}
-		data->serialize(os, version, disk);
+		data->serialize(os, version, disk, formspec_prepend);
 	}
 }
 
diff --git a/src/nodemetadata.h b/src/nodemetadata.h
index 17e47013f..04c3cad90 100644
--- a/src/nodemetadata.h
+++ b/src/nodemetadata.h
@@ -40,7 +40,8 @@ public:
 	NodeMetadata(IItemDefManager *item_def_mgr);
 	~NodeMetadata();
 
-	void serialize(std::ostream &os, u8 version, bool disk=true) const;
+	void serialize(std::ostream &os, u8 version, bool disk=true,
+		std::string formspec_prepend="") const;
 	void deSerialize(std::istream &is, u8 version);
 
 	void clear();
@@ -82,7 +83,7 @@ public:
 	~NodeMetadataList();
 
 	void serialize(std::ostream &os, u8 blockver, bool disk = true,
-		bool absolute_pos = false) const;
+		bool absolute_pos = false, std::string formspec_prepend = "") const;
 	void deSerialize(std::istream &is, IItemDefManager *item_def_mgr,
 		bool absolute_pos = false);
 
diff --git a/src/object_properties.cpp b/src/object_properties.cpp
index af3c7f26a..2c6a74a6f 100644
--- a/src/object_properties.cpp
+++ b/src/object_properties.cpp
@@ -73,28 +73,62 @@ std::string ObjectProperties::dump()
 	return os.str();
 }
 
-void ObjectProperties::serialize(std::ostream &os) const
+void ObjectProperties::serialize(std::ostream &os, u16 protocol_version) const
 {
-	writeU8(os, 4); // PROTOCOL_VERSION >= 37
+	if (protocol_version > 36)
+		writeU8(os, 4); // PROTOCOL_VERSION >= 37
+	else
+		writeU8(os, 1);
 	writeU16(os, hp_max);
 	writeU8(os, physical);
-	writeF32(os, 0.f); // Removed property (weight)
-	writeV3F32(os, collisionbox.MinEdge);
-	writeV3F32(os, collisionbox.MaxEdge);
-	writeV3F32(os, selectionbox.MinEdge);
-	writeV3F32(os, selectionbox.MaxEdge);
-	writeU8(os, pointable);
-	os << serializeString(visual);
-	writeV3F32(os, visual_size);
-	writeU16(os, textures.size());
-	for (const std::string &texture : textures) {
-		os << serializeString(texture);
+	writeF(os, 0.f, protocol_version); // Removed property (weight)
+	if (protocol_version > 36) {
+		writeV3F32(os, collisionbox.MinEdge);
+		writeV3F32(os, collisionbox.MaxEdge);
+		writeV3F32(os, selectionbox.MinEdge);
+		writeV3F32(os, selectionbox.MaxEdge);
+		writeU8(os, pointable);
+	} else if (pointable) {
+		writeV3F1000(os, selectionbox.MinEdge);
+		writeV3F1000(os, selectionbox.MaxEdge);
+	} else {
+		// A hack to emulate unpointable objects
+		for (u8 i = 0; i < 6; i++)
+			writeF1000(os, 0);
 	}
+
+	// The "wielditem" type isn't exactly the same as "item", however this
+	// is the most similar compatible option
+	if (visual == "item" && protocol_version < 37)
+		os << serializeString("wielditem");
+	else
+		os << serializeString(visual);
+
+	if (protocol_version > 36) {
+		writeV3F32(os, visual_size);
+	} else {
+		writeF1000(os, visual_size.X);
+		writeF1000(os, visual_size.Y);
+	}
+
+	// MT 0.4.15 and below don't have the wield_item property and expect
+	// wield_item to be in textures[0].
+	if (protocol_version < 37 && (visual == "item" || visual == "wielditem") &&
+			!wield_item.empty()) {
+		writeU16(os, 1);
+		os << serializeString(wield_item);
+	} else {
+		writeU16(os, textures.size());
+		for (const std::string &texture : textures) {
+			os << serializeString(texture);
+		}
+	}
+
 	writeV2S16(os, spritediv);
 	writeV2S16(os, initial_sprite_basepos);
 	writeU8(os, is_visible);
 	writeU8(os, makes_footstep_sound);
-	writeF32(os, automatic_rotate);
+	writeF(os, automatic_rotate, protocol_version);
 	// Added in protocol version 14
 	os << serializeString(mesh);
 	writeU16(os, colors.size());
@@ -102,16 +136,21 @@ void ObjectProperties::serialize(std::ostream &os) const
 		writeARGB8(os, color);
 	}
 	writeU8(os, collideWithObjects);
-	writeF32(os, stepheight);
+	writeF(os, stepheight, protocol_version);
 	writeU8(os, automatic_face_movement_dir);
-	writeF32(os, automatic_face_movement_dir_offset);
+	writeF(os, automatic_face_movement_dir_offset, protocol_version);
 	writeU8(os, backface_culling);
 	os << serializeString(nametag);
 	writeARGB8(os, nametag_color);
-	writeF32(os, automatic_face_movement_max_rotation_per_sec);
+	writeF(os, automatic_face_movement_max_rotation_per_sec, protocol_version);
 	os << serializeString(infotext);
 	os << serializeString(wield_item);
 	writeS8(os, glow);
+
+	// Everything after this can use writeF32().
+	if (protocol_version < 37)
+		return;
+
 	writeU16(os, breath_max);
 	writeF32(os, eye_height);
 	writeF32(os, zoom_fov);
diff --git a/src/object_properties.h b/src/object_properties.h
index e68b45e2c..dab826bb4 100644
--- a/src/object_properties.h
+++ b/src/object_properties.h
@@ -65,6 +65,6 @@ struct ObjectProperties
 
 	ObjectProperties();
 	std::string dump();
-	void serialize(std::ostream &os) const;
+	void serialize(std::ostream &os, u16 protocol_version) const;
 	void deSerialize(std::istream &is);
 };
diff --git a/src/server.cpp b/src/server.cpp
index 0c1012cc4..8a00f65be 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -771,7 +771,11 @@ void Server::AsyncRunStep(bool initial_step)
 					// u16 id
 					// std::string data
 					buffer.append(idbuf, sizeof(idbuf));
-					buffer.append(serializeString(aom.datastring));
+					if (client->net_proto_version >= 37 ||
+							aom.legacystring.empty())
+						buffer.append(serializeString(aom.datastring));
+					else
+						buffer.append(serializeString(aom.legacystring));
 				}
 			}
 			/*
@@ -1147,6 +1151,9 @@ void Server::ProcessData(NetworkPacket *pkt)
 			return;
 		}
 
+		RemoteClient *client = getClient(peer_id);
+		if (client)
+			pkt->setProtocolVersion(client->net_proto_version);
 		handleCommand(pkt);
 	} catch (SendFailedException &e) {
 		errorstream << "Server::ProcessData(): SendFailedException: "
@@ -1154,7 +1161,7 @@ void Server::ProcessData(NetworkPacket *pkt)
 				<< std::endl;
 	} catch (PacketError &e) {
 		actionstream << "Server::ProcessData(): PacketError: "
-				<< "what=" << e.what()
+				<< "what=" << e.what() << ", command=" << pkt->getCommand() // TODO: REMOVE COMMAND=
 				<< std::endl;
 	}
 }
@@ -1296,11 +1303,11 @@ void Server::Send(session_t peer_id, NetworkPacket *pkt)
 		clientCommandFactoryTable[pkt->getCommand()].reliable);
 }
 
-void Server::SendMovement(session_t peer_id)
+void Server::SendMovement(session_t peer_id, u16 protocol_version)
 {
 	std::ostringstream os(std::ios_base::binary);
 
-	NetworkPacket pkt(TOCLIENT_MOVEMENT, 12 * sizeof(float), peer_id);
+	NetworkPacket pkt(TOCLIENT_MOVEMENT, 12 * sizeof(float), peer_id, protocol_version);
 
 	pkt << g_settings->getFloat("movement_acceleration_default");
 	pkt << g_settings->getFloat("movement_acceleration_air");
@@ -1335,7 +1342,13 @@ void Server::SendPlayerHPOrDie(PlayerSAO *playersao, const PlayerHPChangeReason
 void Server::SendHP(session_t peer_id, u16 hp)
 {
 	NetworkPacket pkt(TOCLIENT_HP, 1, peer_id);
-	pkt << hp;
+	// Minetest 0.4 uses 8-bit integers for HPP.
+	if (m_clients.getProtocolVersion(peer_id) >= 37) {
+		pkt << hp;
+	} else {
+		u8 raw_hp = hp & 0xFF;
+		pkt << raw_hp;
+	}
 	Send(&pkt);
 }
 
@@ -1454,6 +1467,9 @@ void Server::SendInventory(PlayerSAO *sao, bool incremental)
 
 void Server::SendChatMessage(session_t peer_id, const ChatMessage &message)
 {
+	NetworkPacket legacypkt(TOCLIENT_CHAT_MESSAGE_OLD, 0, peer_id);
+	legacypkt << message.message;
+
 	NetworkPacket pkt(TOCLIENT_CHAT_MESSAGE, 0, peer_id);
 	u8 version = 1;
 	u8 type = message.type;
@@ -1464,9 +1480,12 @@ void Server::SendChatMessage(session_t peer_id, const ChatMessage &message)
 		if (!player)
 			return;
 
-		Send(&pkt);
+		if (player->protocol_version < 35)
+			Send(&legacypkt);
+		else
+			Send(&pkt);
 	} else {
-		m_clients.sendToAll(&pkt);
+		m_clients.sendToAllCompat(&pkt, &legacypkt, 35);
 	}
 }
 
@@ -1484,7 +1503,12 @@ void Server::SendShowFormspecMessage(session_t peer_id, const std::string &forms
 		pkt.putLongString("");
 	} else {
 		m_formspec_state_data[peer_id] = formname;
-		pkt.putLongString(formspec);
+		RemotePlayer *player = m_env->getPlayer(peer_id);
+		if (player && player->protocol_version < 37 &&
+				formspec.find("no_prepend[]") == std::string::npos)
+			pkt.putLongString(formspec + player->formspec_prepend);
+		else
+			pkt.putLongString(formspec);
 	}
 	pkt << formname;
 
@@ -1522,7 +1546,7 @@ void Server::SendSpawnParticle(session_t peer_id, u16 protocol_version,
 	}
 	assert(protocol_version != 0);
 
-	NetworkPacket pkt(TOCLIENT_SPAWN_PARTICLE, 0, peer_id);
+	NetworkPacket pkt(TOCLIENT_SPAWN_PARTICLE, 0, peer_id, protocol_version);
 
 	{
 		// NetworkPacket and iostreams are incompatible...
@@ -1569,7 +1593,7 @@ void Server::SendAddParticleSpawner(session_t peer_id, u16 protocol_version,
 	}
 	assert(protocol_version != 0);
 
-	NetworkPacket pkt(TOCLIENT_ADD_PARTICLESPAWNER, 100, peer_id);
+	NetworkPacket pkt(TOCLIENT_ADD_PARTICLESPAWNER, 100, peer_id, protocol_version);
 
 	pkt << p.amount << p.time << p.minpos << p.maxpos << p.minvel
 		<< p.maxvel << p.minacc << p.maxacc << p.minexptime << p.maxexptime
@@ -1604,7 +1628,7 @@ void Server::SendDeleteParticleSpawner(session_t peer_id, u32 id)
 
 void Server::SendHUDAdd(session_t peer_id, u32 id, HudElement *form)
 {
-	NetworkPacket pkt(TOCLIENT_HUDADD, 0 , peer_id);
+	NetworkPacket pkt(TOCLIENT_HUDADD, 0 , peer_id, m_clients.getProtocolVersion(peer_id));
 
 	pkt << id << (u8) form->type << form->pos << form->name << form->scale
 			<< form->text << form->number << form->item << form->dir
@@ -1623,7 +1647,7 @@ void Server::SendHUDRemove(session_t peer_id, u32 id)
 
 void Server::SendHUDChange(session_t peer_id, u32 id, HudElementStat stat, void *value)
 {
-	NetworkPacket pkt(TOCLIENT_HUDCHANGE, 0, peer_id);
+	NetworkPacket pkt(TOCLIENT_HUDCHANGE, 0, peer_id, m_clients.getProtocolVersion(peer_id));
 	pkt << id << (u8) stat;
 
 	switch (stat) {
@@ -1735,7 +1759,8 @@ void Server::SendSetStars(session_t peer_id, const StarParams &params)
 
 void Server::SendCloudParams(session_t peer_id, const CloudParams &params)
 {
-	NetworkPacket pkt(TOCLIENT_CLOUD_PARAMS, 0, peer_id);
+	NetworkPacket pkt(TOCLIENT_CLOUD_PARAMS, 0, peer_id,
+		m_clients.getProtocolVersion(peer_id));
 	pkt << params.density << params.color_bright << params.color_ambient
 			<< params.height << params.thickness << params.speed;
 	Send(&pkt);
@@ -1754,15 +1779,20 @@ void Server::SendOverrideDayNightRatio(session_t peer_id, bool do_override,
 
 void Server::SendTimeOfDay(session_t peer_id, u16 time, f32 time_speed)
 {
-	NetworkPacket pkt(TOCLIENT_TIME_OF_DAY, 0, peer_id);
-	pkt << time << time_speed;
+	if (peer_id != PEER_ID_INEXISTENT) {
+		NetworkPacket pkt(TOCLIENT_TIME_OF_DAY, 0, peer_id,
+			m_clients.getProtocolVersion(peer_id));
+		pkt << time << time_speed;
 
-	if (peer_id == PEER_ID_INEXISTENT) {
-		m_clients.sendToAll(&pkt);
-	}
-	else {
 		Send(&pkt);
+		return;
 	}
+
+	NetworkPacket pkt(TOCLIENT_TIME_OF_DAY, 0, peer_id, 37);
+	NetworkPacket legacypkt(TOCLIENT_TIME_OF_DAY, 0, peer_id, 32);
+	pkt << time << time_speed;
+	legacypkt << time << time_speed;
+	m_clients.sendToAllCompat(&pkt, &legacypkt, 37);
 }
 
 void Server::SendPlayerHP(session_t peer_id)
@@ -1792,7 +1822,7 @@ void Server::SendMovePlayer(session_t peer_id)
 	PlayerSAO *sao = player->getPlayerSAO();
 	assert(sao);
 
-	NetworkPacket pkt(TOCLIENT_MOVE_PLAYER, sizeof(v3f) + sizeof(f32) * 2, peer_id);
+	NetworkPacket pkt(TOCLIENT_MOVE_PLAYER, sizeof(v3f) + sizeof(f32) * 2, peer_id, player->protocol_version);
 	pkt << sao->getBasePosition() << sao->getLookPitch() << sao->getRotation().Y;
 
 	{
@@ -1821,7 +1851,7 @@ void Server::SendLocalPlayerAnimations(session_t peer_id, v2s32 animation_frames
 		f32 animation_speed)
 {
 	NetworkPacket pkt(TOCLIENT_LOCAL_PLAYER_ANIMATIONS, 0,
-		peer_id);
+		peer_id, m_clients.getProtocolVersion(peer_id));
 
 	pkt << animation_frames[0] << animation_frames[1] << animation_frames[2]
 			<< animation_frames[3] << animation_speed;
@@ -1831,7 +1861,7 @@ void Server::SendLocalPlayerAnimations(session_t peer_id, v2s32 animation_frames
 
 void Server::SendEyeOffset(session_t peer_id, v3f first, v3f third)
 {
-	NetworkPacket pkt(TOCLIENT_EYE_OFFSET, 0, peer_id);
+	NetworkPacket pkt(TOCLIENT_EYE_OFFSET, 0, peer_id, m_clients.getProtocolVersion(peer_id));
 	pkt << first << third;
 	Send(&pkt);
 }
@@ -1864,7 +1894,12 @@ void Server::SendPlayerInventoryFormspec(session_t peer_id)
 		return;
 
 	NetworkPacket pkt(TOCLIENT_INVENTORY_FORMSPEC, 0, peer_id);
-	pkt.putLongString(player->inventory_formspec);
+	if (player->protocol_version < 37 && player->inventory_formspec.find(
+			"no_prepend[]") == std::string::npos)
+		pkt.putLongString(player->inventory_formspec +
+			player->formspec_prepend);
+	else
+		pkt.putLongString(player->inventory_formspec);
 
 	Send(&pkt);
 }
@@ -1875,6 +1910,10 @@ void Server::SendPlayerFormspecPrepend(session_t peer_id)
 	assert(player);
 	if (player->getPeerId() == PEER_ID_INEXISTENT)
 		return;
+	if (player->protocol_version < 37) {
+		SendPlayerInventoryFormspec(peer_id);
+		return;
+	}
 
 	NetworkPacket pkt(TOCLIENT_FORMSPEC_PREPEND, 0, peer_id);
 	pkt << player->formspec_prepend;
@@ -1995,6 +2034,10 @@ void Server::SendActiveObjectMessages(session_t peer_id, const std::string &data
 
 void Server::SendCSMRestrictionFlags(session_t peer_id)
 {
+	const u16 protocol_version = m_clients.getProtocolVersion(peer_id);
+	if (protocol_version < 35 && protocol_version != 0)
+		return;
+
 	NetworkPacket pkt(TOCLIENT_CSM_RESTRICTION_FLAGS,
 		sizeof(m_csm_restriction_flags) + sizeof(m_csm_restriction_noderange), peer_id);
 	pkt << m_csm_restriction_flags << m_csm_restriction_noderange;
@@ -2086,17 +2129,29 @@ s32 Server::playSound(const SimpleSoundSpec &spec,
 
 	float gain = params.gain * spec.gain;
 	NetworkPacket pkt(TOCLIENT_PLAY_SOUND, 0);
+	NetworkPacket legacypkt(TOCLIENT_PLAY_SOUND, 0, PEER_ID_INEXISTENT, 32);
 	pkt << id << spec.name << gain
 			<< (u8) params.type << pos << params.object
 			<< params.loop << params.fade << params.pitch
 			<< ephemeral;
+	legacypkt << id << spec.name << gain
+			<< (u8) params.type << pos << params.object
+			<< params.loop << params.fade;
 
 	bool as_reliable = !ephemeral;
+	bool play_sound = gain > 0;
 
 	for (const u16 dst_client : dst_clients) {
+		const u16 protocol_version = m_clients.getProtocolVersion(dst_client);
+		if (!play_sound && protocol_version < 32)
+			continue;
 		if (psound)
 			psound->clients.insert(dst_client);
-		m_clients.send(dst_client, 0, &pkt, as_reliable);
+
+		if (protocol_version >= 37)
+			m_clients.send(dst_client, 0, &pkt, as_reliable);
+		else
+			m_clients.send(dst_client, 0, &legacypkt, as_reliable);
 	}
 	return id;
 }
@@ -2257,6 +2312,13 @@ void Server::sendMetadataChanged(const std::list<v3s16> &meta_updates, float far
 		if (!client)
 			continue;
 
+		if (client->net_proto_version < 37) {
+			for (const v3s16 &pos : meta_updates) {
+				client->SetBlockNotSent(getNodeBlockPos(pos));
+			}
+			continue;
+		}
+
 		ServerActiveObject *player = m_env->getActiveObject(i);
 		v3f player_pos = player ? player->getBasePosition() : v3f();
 
@@ -2303,7 +2365,12 @@ void Server::SendBlockNoLock(session_t peer_id, MapBlock *block, u8 ver,
 	*/
 
 	std::ostringstream os(std::ios_base::binary);
-	block->serialize(os, ver, false);
+
+	RemotePlayer *player = m_env->getPlayer(peer_id);
+	if (player && player->protocol_version < 37)
+		block->serialize(os, ver, false, player->formspec_prepend);
+	else
+		block->serialize(os, ver, false);
 	block->serializeNetworkSpecific(os);
 	std::string s = os.str();
 
@@ -2483,7 +2550,10 @@ void Server::fillMediaCache()
 	std::vector<std::string> paths;
 	m_modmgr->getModsMediaPaths(paths);
 	fs::GetRecursiveDirs(paths, m_gamespec.path + DIR_DELIM + "textures");
-	fs::GetRecursiveDirs(paths, porting::path_user + DIR_DELIM + "textures" + DIR_DELIM + "server");
+	fs::GetRecursiveDirs(paths, porting::path_user + DIR_DELIM + "textures" +
+			DIR_DELIM + "server");
+	fs::GetRecursiveDirs(paths, porting::path_share + DIR_DELIM + "builtin" +
+			DIR_DELIM + "game" + DIR_DELIM + "models");
 
 	// Collect media file information from paths into cache
 	for (const std::string &mediapath : paths) {
@@ -2645,7 +2715,9 @@ void Server::sendRequestedMedia(session_t peer_id,
 void Server::sendDetachedInventory(Inventory *inventory, const std::string &name, session_t peer_id)
 {
 	NetworkPacket pkt(TOCLIENT_DETACHED_INVENTORY, 0, peer_id);
+	NetworkPacket legacy_pkt(TOCLIENT_DETACHED_INVENTORY, 0, peer_id);
 	pkt << name;
+	legacy_pkt << name;
 
 	if (!inventory) {
 		pkt << false; // Remove inventory
@@ -2660,12 +2732,25 @@ void Server::sendDetachedInventory(Inventory *inventory, const std::string &name
 		const std::string &os_str = os.str();
 		pkt << static_cast<u16>(os_str.size()); // HACK: to keep compatibility with 5.0.0 clients
 		pkt.putRawString(os_str);
+		legacy_pkt.putRawString(os_str);
 	}
 
-	if (peer_id == PEER_ID_INEXISTENT)
-		m_clients.sendToAll(&pkt);
-	else
-		Send(&pkt);
+	if (peer_id == PEER_ID_INEXISTENT) {
+		m_clients.newSendToAll(&pkt);
+		if (inventory)
+			m_clients.oldSendToAll(&legacy_pkt);
+	} else {
+		RemoteClient *client = getClientNoEx(peer_id, CS_Created);
+		if (!client) {
+			warningstream << "Could not get client in sendDetachedInventory!"
+				<< std::endl;
+		}
+
+		if (!client || client->net_proto_version >= 37)
+			Send(&pkt);
+		else if (inventory)
+			Send(&legacy_pkt);
+	}
 }
 
 void Server::sendDetachedInventories(session_t peer_id, bool incremental)
@@ -2774,7 +2859,7 @@ void Server::acceptAuth(session_t peer_id, bool forSudoMode)
 	if (!forSudoMode) {
 		RemoteClient* client = getClient(peer_id, CS_Invalid);
 
-		NetworkPacket resp_pkt(TOCLIENT_AUTH_ACCEPT, 1 + 6 + 8 + 4, peer_id);
+		NetworkPacket resp_pkt(TOCLIENT_AUTH_ACCEPT, 1 + 6 + 8 + 4, peer_id, client->net_proto_version);
 
 		// Right now, the auth mechs don't change between login and sudo mode.
 		u32 sudo_auth_mechs = client->allowed_auth_mechs;
diff --git a/src/server.h b/src/server.h
index 52ca1ca3f..40b083272 100644
--- a/src/server.h
+++ b/src/server.h
@@ -374,7 +374,7 @@ private:
 
 	void init();
 
-	void SendMovement(session_t peer_id);
+	void SendMovement(session_t peer_id, u16 protocol_version);
 	void SendHP(session_t peer_id, u16 hp);
 	void SendBreath(session_t peer_id, u16 breath);
 	void SendAccessDenied(session_t peer_id, AccessDeniedCode reason,
diff --git a/src/server/luaentity_sao.cpp b/src/server/luaentity_sao.cpp
index 7b7b7b6c0..e99f56851 100644
--- a/src/server/luaentity_sao.cpp
+++ b/src/server/luaentity_sao.cpp
@@ -117,9 +117,10 @@ void LuaEntitySAO::step(float dtime, bool send_recommended)
 	if(!m_properties_sent)
 	{
 		m_properties_sent = true;
-		std::string str = getPropertyPacket();
+		std::string str = getPropertyPacket(37);
+		std::string legacy_str = getPropertyPacket(32);
 		// create message and add to list
-		m_messages_out.emplace(getId(), true, str);
+		m_messages_out.emplace(getId(), true, str, legacy_str);
 	}
 
 	// If attached, check that our parent is still there. If it isn't, detach.
@@ -228,19 +229,26 @@ std::string LuaEntitySAO::getClientInitializationData(u16 protocol_version)
 	os << serializeString(""); // name
 	writeU8(os, 0); // is_player
 	writeU16(os, getId()); //id
-	writeV3F32(os, m_base_position);
-	writeV3F32(os, m_rotation);
+	writeV3F(os, m_base_position, protocol_version);
+	if (protocol_version >= 37)
+		writeV3F32(os, m_rotation);
+	else
+		writeF1000(os, m_rotation.Y);
 	writeU16(os, m_hp);
 
 	std::ostringstream msg_os(std::ios::binary);
-	msg_os << serializeLongString(getPropertyPacket()); // message 1
+	msg_os << serializeLongString(getPropertyPacket(
+		protocol_version)); // message 1
 	msg_os << serializeLongString(generateUpdateArmorGroupsCommand()); // 2
-	msg_os << serializeLongString(generateUpdateAnimationCommand()); // 3
+	msg_os << serializeLongString(generateUpdateAnimationCommand(
+		protocol_version)); // 3
 	for (const auto &bone_pos : m_bone_position) {
 		msg_os << serializeLongString(generateUpdateBonePositionCommand(
-			bone_pos.first, bone_pos.second.X, bone_pos.second.Y)); // m_bone_position.size
+			bone_pos.first, bone_pos.second.X, bone_pos.second.Y,
+			protocol_version)); // m_bone_position.size
 	}
-	msg_os << serializeLongString(generateUpdateAttachmentCommand()); // 4
+	msg_os << serializeLongString(generateUpdateAttachmentCommand(
+		protocol_version)); // 4
 
 	int message_count = 4 + m_bone_position.size();
 
@@ -472,9 +480,9 @@ std::string LuaEntitySAO::getName()
 	return m_init_name;
 }
 
-std::string LuaEntitySAO::getPropertyPacket()
+std::string LuaEntitySAO::getPropertyPacket(const u16 protocol_version)
 {
-	return generateSetPropertiesCommand(m_prop);
+	return generateSetPropertiesCommand(m_prop, protocol_version);
 }
 
 void LuaEntitySAO::sendPosition(bool do_interpolate, bool is_movement_end)
@@ -500,10 +508,23 @@ void LuaEntitySAO::sendPosition(bool do_interpolate, bool is_movement_end)
 		m_rotation,
 		do_interpolate,
 		is_movement_end,
-		update_interval
+		update_interval,
+		37
 	);
+
+	std::string legacy_str = generateUpdatePositionCommand(
+		m_base_position,
+		m_velocity,
+		m_acceleration,
+		m_rotation,
+		do_interpolate,
+		is_movement_end,
+		update_interval,
+		32
+	);
+
 	// create message and add to list
-	m_messages_out.emplace(getId(), false, str);
+	m_messages_out.emplace(getId(), false, str, legacy_str);
 }
 
 bool LuaEntitySAO::getCollisionBox(aabb3f *toset) const
diff --git a/src/server/luaentity_sao.h b/src/server/luaentity_sao.h
index 3cae2a636..708639941 100644
--- a/src/server/luaentity_sao.h
+++ b/src/server/luaentity_sao.h
@@ -71,7 +71,7 @@ public:
 	bool collideWithObjects() const;
 
 private:
-	std::string getPropertyPacket();
+	std::string getPropertyPacket(const u16 protocol_version);
 	void sendPosition(bool do_interpolate, bool is_movement_end);
 	std::string generateSetTextureModCommand() const;
 	static std::string generateSetSpriteCommand(v2s16 p, u16 num_frames,
diff --git a/src/server/player_sao.cpp b/src/server/player_sao.cpp
index 2f0fa397f..912b4f27e 100644
--- a/src/server/player_sao.cpp
+++ b/src/server/player_sao.cpp
@@ -112,20 +112,37 @@ std::string PlayerSAO::getClientInitializationData(u16 protocol_version)
 	os << serializeString(m_player->getName()); // name
 	writeU8(os, 1); // is_player
 	writeS16(os, getId()); // id
-	writeV3F32(os, m_base_position);
-	writeV3F32(os, m_rotation);
-	writeU16(os, getHP());
+	if (protocol_version >= 37) {
+		writeV3F32(os, m_base_position);
+		writeV3F32(os, m_rotation);
+		writeU16(os, getHP());
+	} else {
+		writeV3F1000(os, m_base_position + v3f(0, BS, 0));
+		writeF1000(os, m_rotation.Y);
+
+		// HP is sent as a signed integer
+		const u16 hp = getHP();
+		if (hp > S16_MAX)
+			writeS16(os, S16_MAX);
+		else
+			writeS16(os, static_cast<s16>(hp));
+	}
 
 	std::ostringstream msg_os(std::ios::binary);
-	msg_os << serializeLongString(getPropertyPacket()); // message 1
+	msg_os << serializeLongString(getPropertyPacket(
+		protocol_version)); // message 1
 	msg_os << serializeLongString(generateUpdateArmorGroupsCommand()); // 2
-	msg_os << serializeLongString(generateUpdateAnimationCommand()); // 3
+	msg_os << serializeLongString(generateUpdateAnimationCommand(
+		protocol_version)); // 3
 	for (const auto &bone_pos : m_bone_position) {
 		msg_os << serializeLongString(generateUpdateBonePositionCommand(
-			bone_pos.first, bone_pos.second.X, bone_pos.second.Y)); // m_bone_position.size
+			bone_pos.first, bone_pos.second.X, bone_pos.second.Y,
+			protocol_version)); // m_bone_position.size
 	}
-	msg_os << serializeLongString(generateUpdateAttachmentCommand()); // 4
-	msg_os << serializeLongString(generateUpdatePhysicsOverrideCommand()); // 5
+	msg_os << serializeLongString(generateUpdateAttachmentCommand(
+		protocol_version)); // 4
+	msg_os << serializeLongString(generateUpdatePhysicsOverrideCommand(
+		protocol_version)); // 5
 
 	int message_count = 5 + m_bone_position.size();
 
@@ -221,9 +238,10 @@ void PlayerSAO::step(float dtime, bool send_recommended)
 
 	if (!m_properties_sent) {
 		m_properties_sent = true;
-		std::string str = getPropertyPacket();
+		std::string str = getPropertyPacket(37);
+		std::string legacy_str = getPropertyPacket(32);
 		// create message and add to list
-		m_messages_out.emplace(getId(), true, str);
+		m_messages_out.emplace(getId(), true, str, legacy_str);
 		m_env->getScriptIface()->player_event(this, "properties_changed");
 	}
 
@@ -286,30 +304,45 @@ void PlayerSAO::step(float dtime, bool send_recommended)
 			m_rotation,
 			true,
 			false,
-			update_interval
+			update_interval,
+			37
 		);
+
+		std::string legacy_str = generateUpdatePositionCommand(
+			pos + v3f(0.0f, BS, 0.0f),
+			v3f(0.0f, 0.0f, 0.0f),
+			v3f(0.0f, 0.0f, 0.0f),
+			m_rotation,
+			true,
+			false,
+			update_interval,
+			32
+		);
+
 		// create message and add to list
-		m_messages_out.emplace(getId(), false, str);
+		m_messages_out.emplace(getId(), false, str, legacy_str);
 	}
 
 	if (!m_physics_override_sent) {
 		m_physics_override_sent = true;
 		// create message and add to list
-		m_messages_out.emplace(getId(), true, generateUpdatePhysicsOverrideCommand());
+		m_messages_out.emplace(getId(), true,
+			generateUpdatePhysicsOverrideCommand(37),
+			generateUpdatePhysicsOverrideCommand(32));
 	}
 
 	sendOutdatedData();
 }
 
-std::string PlayerSAO::generateUpdatePhysicsOverrideCommand() const
+std::string PlayerSAO::generateUpdatePhysicsOverrideCommand(const u16 protocol_version) const
 {
 	std::ostringstream os(std::ios::binary);
 	// command
 	writeU8(os, AO_CMD_SET_PHYSICS_OVERRIDE);
 	// parameters
-	writeF32(os, m_physics_override_speed);
-	writeF32(os, m_physics_override_jump);
-	writeF32(os, m_physics_override_gravity);
+	writeF(os, m_physics_override_speed, protocol_version);
+	writeF(os, m_physics_override_jump, protocol_version);
+	writeF(os, m_physics_override_gravity, protocol_version);
 	// these are sent inverted so we get true when the server sends nothing
 	writeU8(os, !m_physics_override_sneak);
 	writeU8(os, !m_physics_override_sneak_glitch);
@@ -537,10 +570,26 @@ void PlayerSAO::unlinkPlayerSessionAndSave()
 	m_env->removePlayer(m_player);
 }
 
-std::string PlayerSAO::getPropertyPacket()
+std::string PlayerSAO::getPropertyPacket(const u16 protocol_version)
 {
 	m_prop.is_visible = (true);
-	return generateSetPropertiesCommand(m_prop);
+
+	ObjectProperties prop = m_prop;
+	if (protocol_version < 37 && (m_prop.mesh == "3d_armor_character.b3d" ||
+			m_prop.mesh == "character.b3d" ||
+			m_prop.mesh == "skinsdb_3d_armor_character_5.b3d")) {
+		prop.mesh = "mc_compat_character.b3d";
+		for (u16 i = prop.textures.size(); i < 5; i++) {
+			prop.textures.emplace_back("blank.png");
+		}
+	}
+
+	// Remove a one-node offset from a copy of the object properties for MT 0.4
+	if (protocol_version < 37) {
+		prop.selectionbox.MinEdge.Y -= 1.0f;
+		prop.selectionbox.MaxEdge.Y -= 1.0f;
+	}
+	return generateSetPropertiesCommand(prop, protocol_version);
 }
 
 void PlayerSAO::setMaxSpeedOverride(const v3f &vel)
diff --git a/src/server/player_sao.h b/src/server/player_sao.h
index fae7fd079..2d351fdf1 100644
--- a/src/server/player_sao.h
+++ b/src/server/player_sao.h
@@ -180,9 +180,10 @@ public:
 	inline Metadata &getMeta() { return m_meta; }
 
 private:
-	std::string getPropertyPacket();
+	std::string getPropertyPacket(const u16 protocol_version);
 	void unlinkPlayerSessionAndSave();
-	std::string generateUpdatePhysicsOverrideCommand() const;
+	std::string generateUpdatePhysicsOverrideCommand(
+			const u16 protocol_version) const;
 
 	RemotePlayer *m_player = nullptr;
 	session_t m_peer_id = 0;
diff --git a/src/server/unit_sao.cpp b/src/server/unit_sao.cpp
index 2890448cc..2700896ee 100644
--- a/src/server/unit_sao.cpp
+++ b/src/server/unit_sao.cpp
@@ -99,24 +99,34 @@ void UnitSAO::sendOutdatedData()
 	if (!m_animation_sent) {
 		m_animation_sent = true;
 		m_animation_speed_sent = true;
-		m_messages_out.emplace(getId(), true, generateUpdateAnimationCommand());
+		m_messages_out.emplace(getId(), true,
+			generateUpdateAnimationCommand(37),
+			generateUpdateAnimationCommand(32));
 	} else if (!m_animation_speed_sent) {
 		// Animation speed is also sent when 'm_animation_sent == false'
 		m_animation_speed_sent = true;
-		m_messages_out.emplace(getId(), true, generateUpdateAnimationSpeedCommand());
+		m_messages_out.emplace(getId(), true,
+			generateUpdateAnimationSpeedCommand(),
+			// MT 0.4 has no update animation speed command
+			generateUpdateAnimationCommand(32));
 	}
 
 	if (!m_bone_position_sent) {
 		m_bone_position_sent = true;
 		for (const auto &bone_pos : m_bone_position) {
-			m_messages_out.emplace(getId(), true, generateUpdateBonePositionCommand(
-				bone_pos.first, bone_pos.second.X, bone_pos.second.Y));
+			std::string str = generateUpdateBonePositionCommand(
+				bone_pos.first, bone_pos.second.X, bone_pos.second.Y, 37);
+			std::string legacy_str = generateUpdateBonePositionCommand(
+				bone_pos.first, bone_pos.second.X, bone_pos.second.Y, 32);
+			m_messages_out.emplace(getId(), true, str, legacy_str);
 		}
 	}
 
 	if (!m_attachment_sent) {
 		m_attachment_sent = true;
-		m_messages_out.emplace(getId(), true, generateUpdateAttachmentCommand());
+		m_messages_out.emplace(getId(), true,
+			generateUpdateAttachmentCommand(37),
+			generateUpdateAttachmentCommand(32));
 	}
 }
 // clang-format on
@@ -235,7 +245,7 @@ void UnitSAO::notifyObjectPropertiesModified()
 	m_properties_sent = false;
 }
 
-std::string UnitSAO::generateUpdateAttachmentCommand() const
+std::string UnitSAO::generateUpdateAttachmentCommand(const u16 protocol_version) const
 {
 	std::ostringstream os(std::ios::binary);
 	// command
@@ -243,21 +253,37 @@ std::string UnitSAO::generateUpdateAttachmentCommand() const
 	// parameters
 	writeS16(os, m_attachment_parent_id);
 	os << serializeString(m_attachment_bone);
-	writeV3F32(os, m_attachment_position);
-	writeV3F32(os, m_attachment_rotation);
+
+	// Add/remove offsets to compensate for MT 0.4
+	if (protocol_version >= 37) {
+		writeV3F32(os, m_attachment_position);
+	} else {
+		v3f compat_attachment_position = m_attachment_position;
+		if (getType() == ACTIVEOBJECT_TYPE_PLAYER) {
+			compat_attachment_position.Y += BS;
+		} else {
+			ServerActiveObject *p =
+					m_env->getActiveObject(m_attachment_parent_id);
+			if (p && p->getType() == ACTIVEOBJECT_TYPE_PLAYER)
+				compat_attachment_position.Y -= BS;
+		}
+		writeV3F1000(os, compat_attachment_position);
+	}
+
+	writeV3F(os, m_attachment_rotation, protocol_version);
 	return os.str();
 }
 
-std::string UnitSAO::generateUpdateBonePositionCommand(
-		const std::string &bone, const v3f &position, const v3f &rotation)
+std::string UnitSAO::generateUpdateBonePositionCommand(const std::string &bone,
+		const v3f &position, const v3f &rotation, const u16 protocol_version)
 {
 	std::ostringstream os(std::ios::binary);
 	// command
 	writeU8(os, AO_CMD_SET_BONE_POSITION);
 	// parameters
 	os << serializeString(bone);
-	writeV3F32(os, position);
-	writeV3F32(os, rotation);
+	writeV3F(os, position, protocol_version);
+	writeV3F(os, rotation, protocol_version);
 	return os.str();
 }
 
@@ -271,15 +297,15 @@ std::string UnitSAO::generateUpdateAnimationSpeedCommand() const
 	return os.str();
 }
 
-std::string UnitSAO::generateUpdateAnimationCommand() const
+std::string UnitSAO::generateUpdateAnimationCommand(const u16 protocol_version) const
 {
 	std::ostringstream os(std::ios::binary);
 	// command
 	writeU8(os, AO_CMD_SET_ANIMATION);
 	// parameters
-	writeV2F32(os, m_animation_range);
-	writeF32(os, m_animation_speed);
-	writeF32(os, m_animation_blend);
+	writeV2F(os, m_animation_range, protocol_version);
+	writeF(os, m_animation_speed, protocol_version);
+	writeF(os, m_animation_blend, protocol_version);
 	// these are sent inverted so we get true when the server sends nothing
 	writeU8(os, !m_animation_loop);
 	return os.str();
@@ -299,33 +325,38 @@ std::string UnitSAO::generateUpdateArmorGroupsCommand() const
 
 std::string UnitSAO::generateUpdatePositionCommand(const v3f &position,
 		const v3f &velocity, const v3f &acceleration, const v3f &rotation,
-		bool do_interpolate, bool is_movement_end, f32 update_interval)
+		bool do_interpolate, bool is_movement_end, f32 update_interval,
+		const u16 protocol_version)
 {
 	std::ostringstream os(std::ios::binary);
 	// command
 	writeU8(os, AO_CMD_UPDATE_POSITION);
 	// pos
-	writeV3F32(os, position);
+	writeV3F(os, position, protocol_version);
 	// velocity
-	writeV3F32(os, velocity);
+	writeV3F(os, velocity, protocol_version);
 	// acceleration
-	writeV3F32(os, acceleration);
+	writeV3F(os, acceleration, protocol_version);
 	// rotation
-	writeV3F32(os, rotation);
+	if (protocol_version >= 37)
+		writeV3F32(os, rotation);
+	else
+		writeF1000(os, rotation.Y);
 	// do_interpolate
 	writeU8(os, do_interpolate);
 	// is_end_position (for interpolation)
 	writeU8(os, is_movement_end);
 	// update_interval (for interpolation)
-	writeF32(os, update_interval);
+	writeF(os, update_interval, protocol_version);
 	return os.str();
 }
 
-std::string UnitSAO::generateSetPropertiesCommand(const ObjectProperties &prop) const
+std::string UnitSAO::generateSetPropertiesCommand(
+		const ObjectProperties &prop, const u16 protocol_version) const
 {
 	std::ostringstream os(std::ios::binary);
 	writeU8(os, AO_CMD_SET_PROPERTIES);
-	prop.serialize(os);
+	prop.serialize(os, protocol_version);
 	return os.str();
 }
 
@@ -339,7 +370,19 @@ std::string UnitSAO::generatePunchCommand(u16 result_hp) const
 	return os.str();
 }
 
+std::string UnitSAO::generateLegacyPunchCommand(u16 result_hp) const
+{
+	std::ostringstream os(std::ios::binary);
+	// command
+	writeU8(os, AO_CMD_PUNCHED);
+	// result_hp
+	writeU16(os, result_hp);
+	return os.str();
+}
+
 void UnitSAO::sendPunchCommand()
 {
-	m_messages_out.emplace(getId(), true, generatePunchCommand(getHP()));
+	const u16 result_hp = getHP();
+	m_messages_out.emplace(getId(), true, generatePunchCommand(result_hp),
+			generateLegacyPunchCommand(result_hp));
 }
diff --git a/src/server/unit_sao.h b/src/server/unit_sao.h
index 76d409ba6..6e1f2138c 100644
--- a/src/server/unit_sao.h
+++ b/src/server/unit_sao.h
@@ -20,6 +20,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #pragma once
 
+#include "constants.h"
 #include "object_properties.h"
 #include "serveractiveobject.h"
 
@@ -79,16 +80,19 @@ public:
 	void sendOutdatedData();
 
 	// Update packets
-	std::string generateUpdateAttachmentCommand() const;
+	std::string generateUpdateAttachmentCommand(const u16 protocol_version) const;
 	std::string generateUpdateAnimationSpeedCommand() const;
-	std::string generateUpdateAnimationCommand() const;
+	std::string generateUpdateAnimationCommand(const u16 protocol_version) const;
 	std::string generateUpdateArmorGroupsCommand() const;
 	static std::string generateUpdatePositionCommand(const v3f &position,
 			const v3f &velocity, const v3f &acceleration, const v3f &rotation,
-			bool do_interpolate, bool is_movement_end, f32 update_interval);
-	std::string generateSetPropertiesCommand(const ObjectProperties &prop) const;
+			bool do_interpolate, bool is_movement_end, f32 update_interval,
+			const u16 protocol_version);
+	std::string generateSetPropertiesCommand(
+			const ObjectProperties &prop, const u16 protocol_version) const;
 	static std::string generateUpdateBonePositionCommand(const std::string &bone,
-			const v3f &position, const v3f &rotation);
+			const v3f &position, const v3f &rotation,
+			const u16 protocol_version);
 	void sendPunchCommand();
 
 protected:
@@ -112,6 +116,7 @@ private:
 	void onDetach(int parent_id);
 
 	std::string generatePunchCommand(u16 result_hp) const;
+	std::string generateLegacyPunchCommand(u16 result_hp) const;
 
 	// Armor groups
 	bool m_armor_groups_sent = false;
diff --git a/src/sound.h b/src/sound.h
index 090b240c4..bda0780b0 100644
--- a/src/sound.h
+++ b/src/sound.h
@@ -40,6 +40,12 @@ struct SimpleSoundSpec
 	void serialize(std::ostream &os, u8 cf_version) const
 	{
 		os << serializeString(name);
+		if (cf_version < 13) {
+			writeF1000(os, gain);
+			if (cf_version > 10)
+				writeF1000(os, pitch);
+			return;
+		}
 		writeF32(os, gain);
 		writeF32(os, pitch);
 		writeF32(os, fade);
diff --git a/src/tileanimation.cpp b/src/tileanimation.cpp
index a78cb8cb3..a44d8be35 100644
--- a/src/tileanimation.cpp
+++ b/src/tileanimation.cpp
@@ -21,15 +21,27 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 void TileAnimationParams::serialize(std::ostream &os, u8 tiledef_version) const
 {
+	if (tiledef_version < 3 && type != TAT_VERTICAL_FRAMES) {
+		writeU8(os, TAT_NONE);
+		writeU16(os, 1);
+		writeU16(os, 1);
+		writeF1000(os, 1.0f);
+		return;
+	}
+
 	writeU8(os, type);
+
+	// Approximate protocol version
+	const u16 protocol_version = tiledef_version >= 6 ? 37 : 32;
+
 	if (type == TAT_VERTICAL_FRAMES) {
 		writeU16(os, vertical_frames.aspect_w);
 		writeU16(os, vertical_frames.aspect_h);
-		writeF32(os, vertical_frames.length);
+		writeF(os, vertical_frames.length, protocol_version);
 	} else if (type == TAT_SHEET_2D) {
 		writeU8(os, sheet_2d.frames_w);
 		writeU8(os, sheet_2d.frames_h);
-		writeF32(os, sheet_2d.frame_length);
+		writeF(os, sheet_2d.frame_length, protocol_version);
 	}
 }
 
diff --git a/src/tool.cpp b/src/tool.cpp
index af0434bd5..e956345a5 100644
--- a/src/tool.cpp
+++ b/src/tool.cpp
@@ -58,9 +58,11 @@ void ToolCapabilities::serialize(std::ostream &os, u16 protocol_version) const
 {
 	if (protocol_version >= 38)
 		writeU8(os, 5);
-	else
+	else if (protocol_version == 37)
 		writeU8(os, 4); // proto == 37
-	writeF32(os, full_punch_interval);
+	else
+		writeU8(os, 2); // proto >= 18
+	writeF(os, full_punch_interval, protocol_version);
 	writeS16(os, max_drop_level);
 	writeU32(os, groupcaps.size());
 	for (const auto &groupcap : groupcaps) {
@@ -72,7 +74,7 @@ void ToolCapabilities::serialize(std::ostream &os, u16 protocol_version) const
 		writeU32(os, cap->times.size());
 		for (const auto &time : cap->times) {
 			writeS16(os, time.first);
-			writeF32(os, time.second);
+			writeF(os, time.second, protocol_version);
 		}
 	}