Shape Stealer is a uncommon Creature — Shapeshifter Spirit card from Saviors of Kamigawa (SOK), collector number 55. Current market price: $0.34 (foil $1.99), TCGplayer market prices via Scryfall.
Whenever this creature blocks or becomes blocked by a creature, this creature's base power and toughness become equal to that creature's power and toughness until end of turn.