Polymorph is a rare Sorcery card from Mirage (MIR), collector number 82. Current market price: $2.61, TCGplayer market prices via Scryfall.
Destroy target creature. It can't be regenerated. Its controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield, then shuffles all other cards revealed this way into their library.