Affinity is an artifact-heavy deck built around Urza's Saga, Mox Opal, and cheap artifact support pieces like Mishra's Bauble and Pinnacle Emissary, so Meltdown at X=1 or X=3 can wipe most of their cheap artifacts and support pieces in one sweep, though it won't touch a grown Kappa Cannoneer at mana value 6. Mystical Dispute is only discounted against blue spells like Metallic Rebuke, but remains a useful tax spell against their other threats. Lightning Bolt is weak against Kappa Cannoneer once it grows with ward 4, and their creatures are often protected by cheap counterspells, so trimming Bolt for a sweeper effect is more efficient; keep Fatal Push and Sheoldred's Edict as they still answer key threats and force sacrifices.