Izzet Cauldron leans on Agatha's Soul Cauldron plus Proft's Eidetic Memory to grind through graveyard value and card draw. Rest in Peace exiles every graveyard and any card that would go there, so Agatha's Soul Cauldron has no graveyard cards to exile. It also shuts off Stormchaser's Talent's level 2 recursion, Winternight Stories' harmonize, and Fear of Missing Out's delirium. Spell Snare is strong against their mana value 2 plays: Fear of Missing Out, Agatha's Soul Cauldron and Proft's Eidetic Memory. It does nothing against their one-drops like Stormchaser's Talent or Academic Dispute, which have mana value 1. The extra Change the Equation covers those cheap spells, since it counters anything with mana value 2 or less, including Stormchaser's Talent and Boomerang Basics. It also counters red spells like Vivi Ornitier or Fear of Missing Out with mana value 6 or less. Temporary Lockdown stays in because several of their key permanents (Agatha's Soul Cauldron, Proft's Eidetic Memory, Fear of Missing Out, Stormchaser's Talent and its Otter tokens) have mana value 2 or less and get exiled by it. Field of Ruin is cut because it is slow and hands them a basic land. Erode is cut because it also gives them a basic land. Plunder the Trollshaws and Farewell are cut to make room, since slower draw and a six-mana sweeper are less needed once the cheaper answers come in.

Golgari is a grindy discard-and-removal midrange deck, so countermagic against their mostly-creature/removal suite is weak; trim Change the Equation and Three Steps Ahead for proactive disruption. Duress strips Thoughtseize or Professor Dellian Fel before they can use it, which is huge since you're the control deck here and card advantage matters more than tempo. The extra Beza gives you a resilient, hard-to-kill 4/5 body that out-values their removal-heavy plan and can block Badgermole Cub or Sentinel of the Nameless City. Pinnacle Starcage exiles their cheap permanents like Badgermole Cub and Mutavault (as a land it's unaffected, but the ability activation matters less) while also hitting Unholy Annex if cast early; Erode comes out since Get Lost and Temporary Lockdown already cover removal needs.

Prowess aggro wants to go wide with cheap threats and burn your face; Spell Snare picks off their two-mana plays like Emberheart Challenger and Flow State, since it only hits spells with mana value 2 and can't touch their one-mana burn, cantrips, Swiftspear, Soul-Scar Mage, or Stormchaser's Talent. Knockout Blow is excellent and cheap (effectively W against their red creatures) at killing Monastery Swiftspear, Soul-Scar Mage, or Emberheart Challenger in combat while gaining life. High Noon slows their chaotic spell-slinging plan to one spell a turn, which badly hurts a deck built on chaining cheap cantrips and burn. Supreme Verdict comes out since it's too slow and symmetrical against a low curve that rebuilds instantly, and March is replaced by more efficient/cheaper interaction given the format speed; Field of Ruin trims since they have minimal problematic nonbasics worth blowing up at the cost of tempo.