Discordant Spirit is a rare Creature — Spirit card from Mirage (MIR), collector number 261. Current market price: $0.64, TCGplayer market prices via Scryfall.
At the beginning of each end step, if it's an opponent's turn, put a +1/+1 counter on this creature for each 1 damage dealt to you this turn. At the beginning of your end step, remove all +1/+1 counters from this creature.