Dimir Midrange plays a controlling game with Counterspell, Force of Negation, and Spell Snare backed by card advantage engines like Psychic Frog and Orcish Bowmasters, so you want to lean on discard and resilient threats rather than spells that die to counterspells. Toxic Deluge answers Orcish Bowmasters and Psychic Frog before they snowball with counters, both of which are otherwise hard for you to kill. Inquisition of Kozilek is redundant with Thoughtseize against their similarly discard-vulnerable hand; keep Fatal Push, Thoughtseize, and Kozilek's Command as your core game plan.