Spy Combo wants to fill its graveyard via Balustrade Spy and Winding Way and then reanimate with Dread Return, so an extra Nihil Spellbomb gives us a second way to exile their graveyard and strip Dread Return targets or flashback fuel. Extract a Confession forces a sacrifice that can take down their biggest ramped threat (Troll of Khazad-dum, Lotleth Giant) when they go wide with mana dorks and walls. Cast Down is less valuable here since many of their key threats come down via Dread Return reanimation rather than being cast, so it trims cleanly. We keep our aggressive core intact to race their slower ramp-into-fatties plan.