Dimir Midrange is a blue-heavy control deck full of Counterspell, Thoughtseize, and card selection, so Mystical Dispute is excellent here, coming down as cheap as {U} against their Counterspell or Subtlety. The extra Teferi, Time Raveler is key since it shuts off their ability to hold up Counterspell or Force of Negation on your turn while you deploy threats, and strips their own Teferi-style flexibility. Spell Snare cleanly answers Orcish Bowmasters and Psychic Frog at two mana before they generate value, and Consign to Memory can counter Orcish Bowmasters' triggered ping abilities. Trim slow lands and narrow removal for the density of proactive countermagic.