Affinity is an artifact-dense deck (Mox Opal, Engineered Explosives, Kappa Cannoneer, plus the Construct tokens from Urza's Saga) that Meltdown punishes by wiping their cheap artifacts. Pick X carefully, since it also destroys our own Mishra's Bauble and Cori-Steel Cutter. Tormod's Crypt is a narrow inclusion: its main job is to exile their graveyard in response to Emry, Lurker of the Loch, so Emry has no artifact cards to recast. Consign to Memory is strong here because many of their key spells are colorless (Mishra's Bauble, Engineered Explosives), and it can also counter triggered abilities such as Kappa Cannoneer's, Pinnacle Emissary's, and Weapons Manufacturing's, all for a single blue mana. Kappa Cannoneer itself is blue, so Consign can only hit its trigger, not the spell. Mutagenic Growth and Lava Dart are cut because their creatures (Kappa Cannoneer, Pinnacle Emissary) are either too large to kill with 1 damage or protected by ward, making those slots better spent on targeted artifact hate. Prioritize wiping Urza's Saga's Construct tokens with Meltdown and countering Kappa Cannoneer triggers before it snowballs out of removal range.