Arcane Adaptation is a rare Enchantment card from The List (PLST), collector number XLN-46. Current market price: $3.67, TCGplayer market prices via Scryfall.
As this enchantment enters, choose a creature type. Creatures you control are the chosen type in addition to their other types. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.