Dark Betrayal cleanly answers Sheoldred, the Apocalypse, which punishes our grindy plan, while Witherbloom Charm's sacrifice mode refills our hand and its removal mode (mana value 2 or less) kills Badgermole Cub before it snowballs. Fatal Push adds cheap, efficient removal that synergizes with our sacrifice triggers for revolt. Thoughtseize is less necessary against a deck that grinds rather than relies on one key spell, so trim some copies for proactive removal. Keep the full Witch's Oven/Cauldron Familiar/Mayhem Devil engine intact since it out-grinds their removal-heavy shell over time.

Izzet Cauldron is also a graveyard/value deck leaning on Hearth Elemental and Eddymurk Crab, so Tormod's Crypt disrupts their graveyard synergies and can slow their card advantage engines, though it's mainly a tempo tax here rather than a hard answer since their core is spells, not recursion. Dark Betrayal stays in the sideboard: it only destroys black creatures, and their creatures (Hearth Elemental, Eddymurk Crab, Sunderflock) are red or blue, so it has no targets. This matchup is mostly about racing with our proactive sacrifice plan against their Stubborn Denial and Get Out countermagic and grindy shell. Thoughtseize is weaker since they don't have a single bomb to strip and play more cantrips, so trim. Lively Dirge is slow against their tempo plays, so cut a copy in favor of faster interaction.

UBR wants to Fiery Impulse and Volcanic Spite our small creatures and grind with Deduce and Fable, so bringing in our own Fable of the Mirror-Breaker matches their card advantage engine and gives a resilient token generator plus a late-game copy effect. Witherbloom Charm is a flexible answer here: it can destroy a Fable Goblin Shaman token or a Clue from Deduce (both mana value 0), it can sacrifice a permanent to draw two in response to removal, and its life gain mode buys time against their burn. Fatal Push answers their cheap creatures and early Fable tokens. Dark Betrayal stays in the sideboard because it only hits black creatures, and almost all of their threats are red or blue (the Fable and its tokens are red), so it has almost no legal targets. Thoughtseize loses value since UBR's deck is mostly noncreature, instant-speed and proactive (counterspells, removal, card draw) rather than reliant on a single key card to strip, so we trim it to two fewer effective slots. Greedy Freebooter and the lone Umbral Collar Zealot come out as our weakest sacrifice fodder against a deck full of cheap removal that can snipe our 1- and 2-toughness creatures before they generate value.