Hydroblast and Blue Elemental Blast are excellent here since the opponent's whole deck is red. Use them to counter or destroy Kessig Flamebreather and Guttersnipe before they snowball damage, or to blast a key burn spell. Sneaky Snacker is blue-black rather than red, so the blasts can't answer it. Graveyard hate like Nihil Spellbomb does interact with Sneaky Snacker: its trigger returns the card from the graveyard, so exiling the opponent's graveyard (for example by sacrificing Spellbomb in response to the trigger) stops it from coming back. Spellbomb is still a slow, narrow answer against this fast clock, so the slots go to the blasts instead. Archaeomancer is too slow and clunky against this fast aggressive clock, and the narrow one-ofs are cut for proactive interaction. Prioritize countering or killing Flamebreather/Guttersnipe on sight, since every subsequent spell they cast punishes you.

Dimir Control has no red cards, so Hydroblast and Blue Elemental Blast have no targets and stay in the sideboard. Vandalblast could only hit a Baleful Strix or Mukotai Ambusher, so it stays out too. Dispel is strong insurance to protect your own Counterspell or key threat from their Counterspell/Dispel, and Arms of Hadar (-2/-2 to their creatures) can wipe their 1/1s (Baleful Strix, Spellstutter Sprite, Faerie Seer) if they overextend, though Augur of Bolas is a 1/3 and survives. Suffocating Fumes is largely redundant with Arms of Hadar and Thraben Charm is low-impact here, so both come out. This is a grindy mirror-ish matchup, so prioritize resolving card advantage engines like Mulldrifter and Murmuring Mystic while using Dispel to force through your own key spells.

Spy Combo relies on building a board of small mana dorks and defenders (Overgrown Battlement, Wall of Roots, Saruli Caretaker) and digging with Lead the Stampede and Winding Way to find its big creatures. Arms of Hadar's -2/-2 picks off their smaller creatures like Elves of Deep Shadow, Quirion Ranger, Gatecreeper Vine and Mesmeric Fiend, which trims their mana and setup. The larger defenders (Overgrown Battlement, Wall of Roots, Saruli Caretaker) survive it, so don't expect it to wipe their whole mana base. Crypt Incursion exiles all creature cards from their graveyard (shutting off Dread Return reanimation targets) while gaining you life against their eventual big creature swings. Snuff Out is weak here because it can't target their black key creatures (Balustrade Spy, Lotleth Giant, Troll of Khazad-dum, Mesmeric Fiend). The green creatures it can hit are mostly mana dorks and defenders that aren't worth paying 4 life or a card for, and Arms of Hadar handles some of their small creatures more efficiently than single-target removal. Prioritize disrupting their mana engine early before they can chain Lead the Stampede and Winding Way into a critical mass of threats.