Izzet Affinity is an artifact-and-colorless-spell deck built around Urza lands, Karn, the Great Creator, and colorless threats like Kozilek's Command, so Consign to Memory is superb, countering most of their colorless spells (Giant's Boulder, Kozilek's Command, Karn's abilities are not spells but the deck's colorless creature/artifact spells are prime targets) at just one mana with replicate scaling. Engineered Explosives set for X=0 or X=1 mops up their cheap artifact permanents. Stifle has fewer relevant targets since their engine is spell-based rather than activated-ability-based, so it's cut in favor of the more impactful Consign to Memory, and Erode is trimmed since their creature count is low. Force of Will and Force of Negation stay maxed to fight through their own counterspell suite and stop key threats like The One Ring or Ugin, Eye of the Storms.