magarena/release/Magarena/scripts/Custody_Battle.groovy

[
    new MagicAtUpkeepTrigger() {
        @Override
        public MagicEvent executeTrigger(final MagicGame game,final MagicPermanent permanent,final MagicPlayer upkeepPlayer) {
            final MagicPermanent enchanted = permanent.getEnchantedCreature();
            return enchanted.isController(upkeepPlayer) ?
                new MagicEvent(
                    enchanted,
                    new MagicMayChoice(
                        MagicTargetChoice.SACRIFICE_LAND
                    ),
                    this,
                    "PN may\$ sacrifice a land\$. If you don't, " +
                    upkeepPlayer.getOpponent() + " gains control of SN."
                ) :
                MagicEvent.NONE;
        }
        @Override
        public void executeEvent(final MagicGame game, final MagicEvent event) {
            if (event.isYes()) {
                event.processTargetPermanent(game,new MagicPermanentAction() {
                    public void doAction(final MagicPermanent perm) {
                        game.doAction(new MagicSacrificeAction(perm));
                    }
                });
            } else {
                game.doAction(new MagicGainControlAction(
                    event.getPlayer().getOpponent(),
                    event.getPermanent()
                ));
            }
        }
    }
]