Affinity is almost entirely colorless artifacts and colorless-cost spells like Mox Opal, Mishra's Bauble, and Engineered Explosives, making Consign to Memory an extremely efficient one-mana answer that can even replicate to counter multiple threats in a turn. Rest in Peace does not shut down Urza's Saga's construct-generation value over time, but more importantly denies their graveyard synergies and any recursive plans, while also protecting your own life total from Emry, Lurker of the Loch shenanigans. Orim's Chant does little against a deck that can rebuild via Urza's Saga triggers already on the stack, and Day's Undoing is symmetrical card advantage that helps a deck trying to reload artifacts just as much as you, so cut both. Keep March of Otherworldly Light in as a key answer to Kappa Cannoneer and Urza's Saga itself while relying on Prismatic Ending for Construct tokens, and prioritize disrupting their artifact count to keep Mox Opal and Kappa Cannoneer offline.