This is a durdly ramp-combo deck full of colorless spells and lands, so Mystical Dispute is mediocre value: with no blue spells on their side it costs its full {2}{U}, but it is still a flexible soft counter for a key spell like Kozilek's Command or Emrakul if they tap out of extra mana. The main plan is to deploy Teferi, Time Raveler to force them to act only at sorcery speed (switching off instant-speed Kozilek's Command), and Narset, Parter of Veils to dig for answers. Solitude is your clean answer to Emrakul, since Emrakul only has protection from instants, and Wrath of the Skies sweeps their smaller creatures and artifacts such as Basking Broodscale, Sowing Mycospawn and Eldrazi Spawn tokens. Emrakul's mana value is 13, so don't count on Wrath to deal with it. Surgical Extraction exiles the remaining copies of a card like Urza's Saga or Emrakul from their hand and library once you see one in a graveyard. Ashiok, Dream Render stops Sowing Mycospawn's land search and Urza's Saga chapter III from finding anything. Its -1 also exiles their graveyard, which shuts off Shifting Woodland's delirium and undoes Emrakul's cost reduction. It does not stop Ancient Stirrings or Malevolent Rumble, which look at the top of the library rather than search it. Silence and the Isochron Scepter package are too passive here since this matchup is about proactively answering their threats, not protecting your own tempo plays.

This combo deck wins through Basking Broodscale's Eldrazi Spawn loop with Blade of the Bloodchief, and Consign to Memory is premium here since it counters colorless spells and triggered abilities, letting you counter the Blade of the Bloodchief or Basking Broodscale triggers that drive the loop, or stop a colorless spell like Devourer of Destiny or Kozilek's Command outright. Surgical Extraction needs a target card in a graveyard, so use it once a Blade of the Bloodchief has been countered or destroyed, or once Urza's Saga has been sacrificed, to exile the remaining copies from their graveyard, hand, and library. Ashiok, Dream Render does not stop their Ancient Stirrings/Malevolent Rumble digging, since those look at or reveal cards rather than search. Its static ability does stop Urza's Saga chapter III and Sowing Mycospawn from searching your opponent's library, and its -1 exiles their graveyard. Prismatic Ending and March of Otherworldly Light in the mainboard already answer Blade of the Bloodchief and Basking Broodscale, so this plan supplements rather than replaces your existing interaction.

Izzet Prowess is a low-to-the-ground tempo deck full of one-mana noncreature spells and cheap burn, so High Noon is excellent at choking their ability to chain cantrips and burn in a turn. Consign to Memory counters their key triggered colorless-adjacent plays and any colorless spells, though note it does not hit most of their red/blue spells directly — bring it mainly for its replicate flexibility against Mishra's Bauble and similar. Orim's Chant is too slow since tapping out to protect a turn doesn't stop their hasty creatures or instant-speed burn, and Day's Undoing is risky when they can rebuild a fast hand quickly. Lean on Solitude, Wrath of the Skies, and Supreme Verdict to reset the board against their small creatures.