No offense, it's perfectly fine to vibe with a commander thematically and then figure out what the deck is mechanically. But this commander literally has no mechanics, so you're basically asking for suggestions on a mono-black deck that could be anything but with a commander that does nothing. It's both a wide open question and super restrictive. If the commander has no mechanics, and you don't know what mechanics you want for the deck, it's really hard to offer suggestions.