Izzet Spellementals is a red spell-slinging shell built around Eddymurk Crab and Hearth Elemental, making Flashfreeze a premium answer to their red threats like Slickshot Show-Off and Burst Lightning. Day of Black Sun, cast for a small X, sweeps their early creatures before they can chain spells into a bigger board. Sage of the Skies offers a cheap, resilient flying blocker/clock while you dig for sweepers. Consult the Star Charts and a Duress are too passive against a deck that wants to go over the top with spell-triggered growth, and the extra Deadly Cover-Up is too slow, so those come out.

UR Aggro features key red spells, so Flashfreeze is a blank check against Burst Lightning or Slickshot Show-Off. Day of Black Sun, set for X=2, strips and destroys their small creatures (Slickshot Show-Off, Otter tokens) even before they can protect them, and it comes down faster than the clunkier Deadly Cover-Up. Sage of the Skies gives you a cheap flying lifelink blocker/clock that stabilizes the race. Consult the Star Charts is too slow against this tempo plan and Duress misses their creature threats, so those and Deadly Cover-Up come out for a faster, more proactive plan.

Azorius Tempo is white/blue with no red or green spells, so Flashfreeze stays in the sideboard, but Duress still strips key noncreature pieces like High Noon, Avatar's Wrath, or Airbender Ascension before they matter. Disdainful Stroke is a clean answer to their rare MV4+ spells. Sage of the Skies trades well in the air against their fliers like Aven Interrupter and Skycoach Conductor while gaining life to blunt their tempo plan. Sear and Nowhere to Run are one-for-one removal against a deck with a low individual threat density, and Pest Control has few targets, so those make room.