Repulsive Mutation is a uncommon Instant card from Murders at Karlov Manor (MKM), collector number 227. Current market price: $0.71 (foil $1.05), TCGplayer market prices via Scryfall.
Put X +1/+1 counters on target creature you control. Then counter up to one target spell unless its controller pays mana equal to the greatest power among creatures you control.