Dimir Midrange is a mirror-like matchup full of blue spells (Counterspell, Preordain, Subtlety, Quantum Riddler, Tamiyo), so Mystical Dispute is frequently a two-mana hard counter that can strip away their Counterspell or Force of Negation protecting their own threats. We trim our own copies of Quantum Riddler since it clashes with their Counterspell and Spell Snare-heavy counter suite and doesn't survive their Fatal Push or Orcish Bowmasters pings as easily as our cheaper interaction. Keep Force of Negation and Subtlety at full count to fight through their own counterspell-heavy plan and to bounce their Psychic Frog or Orcish Bowmasters before it snowballs. This is a battle of card quality and countermagic, so prioritize protecting our Crashing Footfalls and Violent Outburst with our own free counters.