Flashfreeze is solid here, countering the red spells: Prismari Charm, Traumatic Critique, Burst Lightning, Impractical Joke, and Hearth Elemental. It can't touch blue-only cards like Eddymurk Crab and Sunderflock, so don't count on it for those. Disdainful Stroke snipes Eddymurk Crab and Sunderflock before they take over the game. Day of Judgment is weak since the opponent's threats grow incrementally and they rebuild quickly with cantrips; cut it along with Pinnacle Starcage, which only exiles artifacts and creatures with mana value 2 or less and has almost nothing to hit beyond Ghost Vacuum, since their real threats cost far more. Keep Countersculpt and No More Lies as premium interaction against their spell-heavy plan.

Flashfreeze counters only red or green spells, so it is a narrower answer than it looks, but it still hits their key plays for two mana: Burst Lightning, Slickshot Show-Off, Impractical Joke, Wild Ride, and the red half of Vibrant Outburst. It cannot touch their blue-only spells like Flow State, Eddymurk Crab, or Elusive Otter. Disdainful Stroke is live against Eddymurk Crab and any high-mana-value threats they bring in from the sideboard, such as Sunspine Lynx. Jace's Machinations is too slow against this fast aggro deck, and Consult the Star Charts is similarly slow. Seam Rip stays in because it checks mana value, so it can exile Slickshot Show-Off (mana value 2) and Elusive Otter no matter how much power they have. Prioritize Get Lost and Day of Judgment to reset the board against their wide, cheap-creature plan.

Disdainful Stroke is great against Kaito, Bane of Nightmares and other four-plus mana value threats this deck brings, while Spell Snare stays in because Dimir has plenty of two-mana-value spells to hit, like Floodpits Drowner, Azure Beastbinder, Bitter Triumph and Shoot the Sheriff. Emeritus of Ideation gives us a large flying threat with ward {2} that can also refill our hand via its instant side. Erode comes out since it can be an awkward one-for-one against cheap creatures like Floodpits Drowner or Spyglass Siren, and Jace's Machinations comes out as a slower, more situational play in this matchup. Keep Get Lost as our premium removal for Kaito and Enduring Curiosity, and keep Seam Rip for cheap targets with mana value 2 or less such as Floodpits Drowner, Spyglass Siren and Dream Beavers. Day of Judgment stays in since Dimir Midrange builds a board of cheap creatures and incremental threats.