We all have that deck that just survives even though it isn't the best. For me that's [[Torgaar, Famine Incarnate]]. It's not the best mono black commander in any way but its particular combination of effects to me is emblematic of mono black. It's a bit of a swiss army knife and so I find myself hard pressed to really change anything about the core of the deck.
[[Selvala, Explorer Returned]] group hug. It's all about just speeding the game up and giving everybody a bunch of stuff. Nobody ever wants to kill Selvala because everyone gets to draw cards. It's so much fun as long as you don't care about winning.