Spy Combo wins by flooding the board with mana dorks and small creatures (Overgrown Battlement, Saruli Caretaker, Wall of Roots) to enable Dread Return into Balustrade Spy loops, so sweeper effects are premium. Arms of Hadar and Drown in Sorrow both wipe out their defenders and most of their 0/x-3/x creature suite, massively slowing their mana engine and combo assembly. Spell Pierce is weak since their key enablers are mostly creatures and sorceries they can often just replay, while Suffocating Fumes' -1/-1 is redundant with the stronger sweepers coming in. Keep Counterspell in to stop a Dread Return reanimation attempt.