Mono-Black Midrange relies on hand disruption (Duress, Cabal Therapy) and efficient threats like Hypnotic Specter and Nantuko Shade, so our own Duress helps strip their removal or disruption before they can use it on us. Smother cleanly answers Hypnotic Specter, Nantuko Shade, and Ravenous Rats, all at mana value 3 or less, which is important since our own removal suite is light on cheap answers to their early beaters. Mulch is cut because they will attack our graveyard-dependent plan less than other decks and we want proactive disruption instead; Unearth loses value since Cabal Therapy and discard effects can strip our small reanimation targets before we use them. Keep Wasteland in to fight their Mishra's Factory and slow their Dark Ritual-fueled starts.