Mono Black Aggro races you with Bloodghast and Gray Merchant of Asphodel, so Witherbloom Charm's instant-speed removal mode kills key mana value 2 or less permanents like Stitcher's Supplier or Dark Matter Manipulator at instant speed, and the life gain mode can swing a close race against their drain plan. Dark Betrayal is tempting but note their own sideboard brings Leyline of the Void, so don't overcommit to graveyard synergies; Fatal Push answers Bloodghast and other cheap threats cleanly. Cut Thoughtseize since mirror-style discard wars favor the proactive deck, and trim a couple Shambling Ghast since this matchup rewards removal and life swings over small sacrifice bodies that trade evenly with their aggressive one-drops.