Gitaxian Anatomist is a common Creature — Phyrexian Wizard card from Phyrexia: All Will Be One (ONE), collector number 52. Current market price: $0.28 (foil $0.14), TCGplayer market prices via Scryfall.
When this creature enters, you may tap it. If you do, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)