Sidisi, Brood Tyrant is a mythic Legendary Creature — Snake Shaman card from Khans of Tarkir (KTK), collector number 199. Current market price: $1.05 (foil $7.82), 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.