Bolass Citadel can enable some broken stuff in any mono-black deck, especially one focused around artifacts
Take the old school Spiritmonger, with regeneration, countering, and shifting color
Its not hard to imagine how quickly doubling the counters on things can get out of hand, so well just leave you to it
I think I have an unnatural bias towards him, but like his brethren Hellspark Elemental, he leans a little more on the burn side of the spectrum than the creature side
At one point, this card was hovering around $700 due to limited printing, whereas it now exists within the realm or mortals
Thelonite Hermit: goes with anything dropping Saproling tokens, and then goes with anything that helps with counters on your creatures or gives you benefit because you have counters on your creatures