Mari, the Killing Quill {1}{B}{B}
Legendary Creature — Vampire Assassin
BlackCommander: legal
Identity
Black
EDHREC rank
#2,613
Cheapest printing
US$5.55
TCGplayer
Printings
3
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."
Keywords: treasure
Every printing
highest TCGplayer market first; a card with only a thin single listing shows its low
In short
A Commander deck is a commander and 99 other cards, one copy of each (except basic lands), all inside the commander's colour identity. Paste a full list into the deck price calculator to price it and check it against the format.