Izzet Spellementals is almost entirely blue and red, so Mystical Dispute is a strong, flexible counter here: it costs only {U} against their blue cantrips and big blue Elementals like Sunderflock and Eddymurk Crab, and it still works as a three-mana soft counter against red spells like Hearth Elemental. Change the Equation answers their cheap interaction and card flow, since its first mode counters any spell with mana value 2 or less (Stubborn Denial, Fiery Impulse, the cantrips), and its second mode counters red spells with mana value 6 or less such as Prismari Charm and Hearth Elemental. It cannot hit the blue Sunderflock or Eddymurk Crab. Spell Snare is too narrow since few of their key cards sit at exactly mana value 2, so swap it for the more flexible Change the Equation. March of Otherworldly Light is a reasonable removal spell for Hearth Elemental and Sunderflock but is less necessary than counters that stop the spell before it resolves, so trim two copies. Temporary Lockdown stays as is, but note that it only exiles nonland permanents with mana value 2 or less, so it does very little against Hearth Elemental, Eddymurk Crab, or Sunderflock, whose mana values are 6, 7, and 9 regardless of cost reductions.