Sidisi, Brood Tyrant is a rare Legendary Creature — Snake Shaman card from Commander Masters (CMM), collector number 355. Current market price: $2.09 (foil $1.81), TCGplayer market prices via Scryfall.
Whenever Sidisi enters or attacks, mill three cards. Whenever one or more creature cards are put into your graveyard from your library, create a 2/2 black Zombie creature token.