Your search for "Biomass Mutation 213/249" revealed the following:
Biomass Mutation (GTC) from Gatecrash, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Dan Murayama Scott Card Text:Creatures you control become X/X until end of turn.
Biomass Mutation - GTC Reprint (PLST) from The List, available at 401 Games Canada. Rarity: Rare Finish: Normal Artist: Dan Murayama Scott Card Text:Creatures you control have base power and toughness X/X until end of turn.