Hydroblast is excellent here, countering any of their red spells or destroying red permanents like Kessig Flamebreather and Guttersnipe outright. Relic of Progenitus and Nihil Spellbomb exile Lava Dart and Faithless Looting from the graveyard before flashback, and they also stop Sneaky Snacker from recurring. They do nothing against madness-cast Fiery Temper since that card is cast from exile. Agony Warp and Debt to the Kami are too narrow against a deck with few relevant creature targets, and Suffocating Fumes only kills their 1-toughness creatures like Voldaren Epicure and Sneaky Snacker, while missing Guttersnipe and Kessig Flamebreather, the creatures that actually matter. Prioritize Snuff Out and Counterspell to control the damage engine, and keep removal focused on Guttersnipe and Kessig Flamebreather.

This is the mirror, so the game is decided by card quality and tempo rather than hate cards. Annul is a reasonable one-mana answer to their Mukotai Ambusher if cast as a spell before ninjutsu, but more relevantly stops nothing else they run, so bring it in lightly as a flexible counter. Spell Pierce loses value since the opponent can usually find two extra mana, and Suffocating Fumes is weak against their 1/3s and 2/2s with higher toughness. Focus on resolving Spellstutter Sprite and Faerie Seer on curve and trading removal efficiently, since both sides have nearly identical removal and counterspell suites.

Arms of Hadar gives their creatures -2/-2, which kills Glint Hawk, Refurbished Familiar, and Baleful Strix, so it can take out several threats at once and is more efficient than single-target removal. Kor Skyfisher survives as a 0/1 and Utrom Monitor is unaffected, so don't count on it as a full sweep. Relic of Progenitus can exile their graveyard in response to Blood Fountain's recursion, and it replaces itself with a card when sacrificed. Debt to the Kami is weak since Affinity floods the board with small threats rather than a single must-remove creature, and Agony Warp is redundant with the other cheap removal already in the deck. Keep Suffocating Fumes in, since -1/-1 can kill their Baleful Strix and Refurbished Familiar.