BRG floods the board with cheap sacrifice-synergy creatures like Callous Inspector, Gene Pollinator, and Greedy Freebooter, so Day of Black Sun sweeps their early board cheaply while your bigger threats survive. Duress strips a key piece like Obsessive Pursuit or Requiting Hex before it can develop, and Deep-Cavern Bat provides an extra lifelink flying blocker while stripping their hand. Cut the narrow Rapid Rescue and Wistfulness, which are too slow against this aggressive sacrifice shell, along with both Awaken the Honored Dead copies and a Bitter Triumph since their creatures are individually low-impact and don't always justify a premium removal spell.

Izzet Spellementals is built around chaining cheap blue and red spells like Prismari Charm and Traumatic Critique into growing threats, so Flashfreeze is a clean answer to those red-blue spells specifically. Duress proactively strips key interaction like Spell Snare or Get Out before they can protect their engine, disrupting their plan before it starts. Wistfulness and Rapid Rescue are too slow against a deck that wants to chain many small spells, and a second Bitter Triumph is less necessary since their real threats (Hearth Elemental, Eddymurk Crab) are usually best answered proactively or with a Terror of the Peaks trigger.

Mono-Green Landfall ramps into big Mossborn Hydra and Mightform Harmonizer threats, so Day of Black Sun sweeps their early mana dorks and small creatures while their landfall payoffs are still developing. Ouroboroid gives you a way to grow your own board quickly to race or stabilize against their bigger threats in a long game. Rapid Rescue's lifegain is marginal against a deck that isn't racing you with direct damage, and a single Bitter Triumph is enough removal since their creatures are mostly vanilla stat-based threats rather than must-kill value engines.