This matchup is entirely about answering their spells before Hearth Elemental and Eddymurk Crab snowball. Flashfreeze directly counters their red spells, such as Hearth Elemental, Prismari Charm, Burst Lightning (kicked or not), and Impractical Joke, since Prismari Charm is blue and red and so counts as red. It can't touch their mono-blue spells like Sleight of Hand, Flow State, Opt, Eddymurk Crab, or Sunderflock. Disdainful Stroke and Negate pick off Sunderflock and Traumatic Critique respectively, their biggest payoffs. Their threats are mana value 6 or higher, so Spell Snare misses the creatures that matter and comes out, along with Duress since their hand holds cantrips, not discardable bombs.