Obsidian Charmaw flies over most of their ground creatures and destroys a nonbasic land on entry, hitting Eldrazi Temple, Ugin's Labyrinth, or Urza's Saga to disrupt their mana and slow combo assembly. Galvanic Discharge is weak here since its max three points of damage from energy doesn't scale against their large Eldrazi like Emrakul, the Promised End or Devourer of Destiny, so it comes out for a bigger flying proactive threat. Keep Solitude to answer their biggest bodies, and keep Wrath of the Skies as a sweeper for their smaller creatures and Spawn tokens. Keep Consign to Memory in since it counters colorless spells like Devourer of Destiny, Kozilek's Command, and Emrakul, the Promised End, and it can also counter their triggered abilities such as the cast triggers on their Eldrazi. Spell Snare still catches two-mana pieces like Malevolent Rumble, Basking Broodscale, and Talisman of Resilience, so the rest of the removal suite stays untouched.

This is a colorless-leaning combo deck, so Mystical Dispute mostly costs the full {2}{U}, but it's still flexible instant-speed countermagic for Kozilek's Command or a big Eldrazi like Devourer of Destiny. Ashiok, Dream Render stops opposing spells and abilities from searching their library, which shuts off Urza's Saga chapter III (their tutor for Blade of the Bloodchief and other cheap artifacts) and the land search on Sowing Mycospawn's cast trigger. It does not touch Ancient Stirrings or Malevolent Rumble, which only look at or reveal the top cards rather than searching, so don't expect Ashiok to slow those down. Teferi, Time Raveler is clunky against a combo deck that wins through activated and triggered abilities rather than casting spells on your turn, and Quantum Riddler is too slow if they assemble the loop early, so both get trimmed. Keep Solitude and Prismatic Ending in since they can exile Basking Broodscale or Glaring Fleshraker before the loop starts, and Spell Snare can counter a Basking Broodscale (mana value 2). Note Galvanic Discharge cannot target the Blade of the Bloodchief equipment itself, so removing the Broodscale creature is the key interaction point.

Mystical Dispute costs just {U} when it targets a blue spell, which against this blue-red Izzet Prowess list means Expressive Iteration or Preordain. Against their red spells, including Cori-Steel Cutter, Lightning Bolt and the creatures, it costs its full {2}{U} and counters the spell unless they pay {3}. Teferi, Time Raveler does limit them to sorcery-speed burn and tricks, but at three mana it is too slow against cheap hasty threats and does nothing about creatures already on the board, so both copies come out. Snapcaster Mage and Ephemerate are too slow against a deck racing with cheap burn and prowess, so one of each is trimmed for interaction. Ashiok, Dream Render is a marginal inclusion: Izzet Prowess plays nine fetchlands, and Ashiok's static ability stops them from searching their library, while its -1 exiles their graveyard, which shuts off the delirium on Dragon's Rage Channeler. Solitude stays in to pick off Dragon's Rage Channeler or Monastery Swiftspear. Consign to Memory is narrow here, since it can only counter triggered abilities or colorless spells, but it can stop Cori-Steel Cutter's Flurry trigger, a prowess or surveil trigger, or a Mishra's Bauble.