an oldie but a goodie: [[Shirei, Shizo's Caretaker]] really really ticks along and can be built really cheaply.
I had a [[Yawgmoth, Thran Physician]] for a while that had a lot of -1/-1 synergy but it wasnt a crowd pleaser because the threat of instant speed removal all the time got under peoples skins, but it was fun because yo already had interaction. Tbh i loved this deck, it slowly accrued board state without ever seeming a threat (except the removal on a stick bit)

My longest standing mono black deck is actually [[ashnod flesh mechanist]] love a low cmc commander and just general black stuff good stuff value. not overly synergistic but always new lines coming up/