Mari, the Killing Quill is a rare Legendary Creature — Vampire Assassin card from New Capenna Commander (NCC), collector number 97. Current market price: $5.47 (foil $6.08), TCGplayer market prices via Scryfall.
Whenever a creature an opponent controls dies, exile it with a hit counter on it. Assassins, Mercenaries, and Rogues you control have deathtouch and "Whenever this creature deals combat damage to a player, you may remove a hit counter from a card that player owns in exile. If you do, draw a card and create two Treasure tokens."