Mystical Dispute is discounted against their heavy blue suite (Deduce, Make Disappear, Negate) and is excellent at stopping their countermagic or Fable of the Mirror-Breaker. Test of Talents strips copies of key instants/sorceries like Indomitable Creativity or Fiery Impulse after countering one, denying rebuys. This is a control mirror where card quality and countering their big plays (Indomitable Creativity, Atraxa, Grand Unifier, Valgavoth, Terror Eater) matters more than cheap removal, so March of Otherworldly Light and some selection are trimmed for proactive counterspells.