Geralf, the Fleshwright is a mythic Legendary Creature — Human Warlock card from Outlaws of Thunder Junction Promos (POTJ), collector number 50p. Current market price: $2.47 (foil $5.99), TCGplayer market prices via Scryfall.
Whenever you cast a spell during your turn other than your first spell that turn, create a 2/2 blue and black Zombie Rogue creature token. Whenever a Zombie you control enters, put a +1/+1 counter on it for each other Zombie that entered the battlefield under your control this turn.