This matchup is a durdly grind where our interaction needs to answer big threats like Emrakul and the Eldrazi Spawn-fueled Urza's Saga/Eldrazi Temple engine rather than cheap spells. Meltdown at X=1-2 cleans up Urza's Saga Constructs, Springleaf Drum, and Vexing Bauble, and X=2 also catches Talisman of Resilience. It only destroys artifacts, so it does nothing to their Eldrazi creatures or lands. Surgical Extraction can strip a second copy of Ancient Stirrings or Malevolent Rumble to disrupt their card selection engine, or exile a key Emrakul after we counter one copy. Spell Snare and Spell Pierce are weaker here because the threats that matter most, Emrakul (mana value 13) and Devourer of Destiny (mana value 7), are creature spells that neither can handle. Spell Snare only catches Kozilek's Command when X=0, and Spell Pierce can target it but their mana development makes the tax easy to pay. They come out in favor of more impactful disruption.

Rakdos Delirium is a graveyard-fueled aggressive deck full of cheap threats and card types to enable Nethergoyf and delirium payoffs, and they bring in graveyard hate and Obsidian Charmaw against us, so we need to race rather than durdle. Meltdown at X=0 destroys their Mishra's Bauble (mana value 0), and at X=1 it also catches Nihil Spellbomb (mana value 1), which would otherwise exile our graveyard and hurt Murktide Regent. Surgical Extraction can strip a key card like Stitcher's Supplier or Street Wraith out of their graveyard engine entirely. Flow State replaces some card selection since our graveyard will naturally fill with instants and sorceries for its upgrade mode; Counterspell gets trimmed since tempo matters more than hard countering midrange threats, and Spell Snare is narrow here, only hitting their two-drops like Fear of Missing Out and Orcish Bowmasters.

Boros Energy is a creature-heavy aggro deck with a modest number of noncreature spells, so Force of Negation, Spell Pierce and Consign to Memory lose value and come out. Consign to Memory in particular only answers triggered abilities and colorless spells. Stern Scolding comes in as a cheap answer to their early creatures: it counters Ragavan, Ocelot Pride, Guide of Souls, Ajani, Nacatl Pariah, Voice of Victory and Seasoned Pyromancer, all of which have power or toughness 2 or less. Fire Magic's Fire mode costs just {R} and deals 1 damage to each creature, which sweeps their 1-toughness creatures and tokens (Ocelot Pride and its Cat tokens, Elemental tokens, Warrior tokens, Ajani's 2/1 Cat Warrior token and their Ragavan) before they snowball. It does not kill the 2/2 Goblin Shaman token from Fable of the Mirror-Breaker, and it also hits our own Dragon's Rage Channeler and Ragavan, so time it carefully. Flow State replaces a weaker counterspell with card selection to find removal and threats against their go-wide board. Spell Snare, Counterspell and the full removal suite (Lightning Bolt, Unholy Heat) stay in to handle their small creatures and Ajani and Fable of the Mirror-Breaker. Meltdown stays in the sideboard because it only destroys artifacts, and their only relevant artifacts here are Treasure tokens. Mystical Dispute also stays out: it costs the full {2}{U} against a deck with no blue spells and only counters if they can't pay {3}, which is too slow against aggro.