Primal Clay is a common Artifact Creature — Shapeshifter card from Masters 25 (A25), collector number 228. Current market price: $0.18 (foil $0.16), TCGplayer market prices via Scryfall.
As this creature enters, it becomes your choice of a 3/3 artifact creature, a 2/2 artifact creature with flying, or a 1/6 Wall artifact creature with defender in addition to its other types. (A creature with defender can't attack.)