Hapatra, Vizier of Poisons is a rare Legendary Creature — Human Cleric card from Amonkhet (AKH), collector number 199. Current market price: $0.42 (foil $7.10), TCGplayer market prices via Scryfall.
Whenever Hapatra deals combat damage to a player, you may put a -1/-1 counter on target creature. Whenever you put one or more -1/-1 counters on a creature, create a 1/1 green Snake creature token with deathtouch.