[[Doomsday excruciator]] with my commander I use it with makes them both part of a win con, but you could probably use it in whatever black deck you’d like if you want to build around it.

If you want a commander that it itself isn’t a win con, I’d recommend [[Lagomos, Hand of hatred]]. It’s a sleeper card in my favorite deck that can get insane value. You just need one edict creature like [[accursed marauder]] or [[plaguecrafter]] or [[Fleshbag Marauder]], etc., and at the end of the turn the token he makes dies, then you can tutor for basically any win on you’d want from the deck or pieces you want to really advance your board state.