magarena/release/Magarena/scripts/Biting_Tether.groovy

[
    new MagicAtUpkeepTrigger() {
        @Override
        public MagicEvent executeTrigger(
                final MagicGame game,
                final MagicPermanent permanent,
                final MagicPlayer upkeepPlayer) {
            return permanent.isController(upkeepPlayer) ?
                new MagicEvent(
                    permanent,
                    permanent.getEnchantedCreature(),
                    this,
                    "PN puts a -1/-1 counter on " +
                    permanent.getEnchantedCreature() + "."
                ) :
                MagicEvent.NONE;
        }

        @Override
        public void executeEvent(
                final MagicGame game,
                final MagicEvent event) {
            game.doAction(new MagicChangeCountersAction(
                event.getRefPermanent(),
                MagicCounterType.MinusOne,1,true
            ));            
        }
    }
]