Sengir, the Dark Baron {4}{B}{B}
Legendary Creature — Vampire Noble
BlackCommander: legal
Identity
Black
EDHREC rank
#11,266
Cheapest printing
US$0.30
TCGplayer
Printings
3
Flying
Whenever another creature dies, put two +1/+1 counters on Sengir.
Whenever another player loses the game, you gain life equal to that player's life total as the turn began.
Partner (You can have two commanders if both have partner.)
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.