Sumo mod by MisterE for use with arena_lib (minigame_lib) You should be familiar with how to set up arena_lib arenas.
Code snippets from https://gitlab.com/zughy-friends-minetest/arena_lib/-/blob/master/DOCS.md and from Zughy's minigames
to set up an arena, create a confined space that floats in the air, with lava or other damage blocks beneath. Set the spawners on the platform. You can use mesecons to make the board more interesting.