Polymorph is a rare Sorcery card from Classic Sixth Edition (6ED), collector number 86. Current market price: $1.47, 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.