Hapatra, Vizier of Poisons [Amonkhet]

Cost: B G Whenever Hapatra, Vizier of Poisons 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. Her subtle smile is suffused with venom.