Technically speaking, it's legal to play with a deck of more than 60 cards, but at all times your deck must be at least 60 cards and your sideboard must be at most 15 cards
Atraxa, Grand Unifier is the poster angel for a multi-format staple, and its premium printings from Phyrexia: All Will Be One arent too far from $100
Its a simpler line, but any reanimation that doesnt already grant haste becomes away better, as suggested by the decks inclusion of Beacon of Unrest and From Under the Floorboards
Making things die is what mono-black does best
Her card here represents all of this well
If you can read from your opponents that they live on self-mill, or rely on a discard outlet, there's an opportunity to make an army out of advisors and win, but otherwise, this is a good way to trigger mill if you like cards such as Deepmuck Desperado, The Water Crystal, and Zellix, Sanity Flayer