Mono-Black Aggro floods the board with cheap one and two mana creatures like Forsaken Miner, Iridescent Vinelasher, and Nighthowl Pursuer, so Day of Black Sun at low X is a clean sweeper against their curve. Ghost Vacuum helps slow down Forsaken Miner's graveyard recursion. Spell Pierce and Spell Snare are narrow counterspells that only stop a fraction of what this deck does, so they come out in favor of a sweeper and graveyard hate; keep your removal suite (Requiting Hex, Bitter Triumph, Shoot the Sheriff) and We Say Thee Nay! since it can counter any of their creature spells and remains one of your best answers to their threats.