Dimir Tempo is a blue-black deck, and most of its key spells are blue, which makes Pyroblast an efficient answer. It can counter their Brainstorm, Ponder, Daze, or Force of Will, or destroy a resolved Bilbo, Kaito, or Brazen Borrower. Their black spells, such as Thoughtseize, Fatal Push, and Orcish Bowmasters, are not blue, so Pyroblast can't touch them. Hydroblast only hits red cards and Dimir plays none, so it stays in the sideboard. Surgical Extraction can exile a Nethergoyf from the graveyard before it escapes, or strip copies of a key card from their hand and library. Boomerang Basics and Flow State are cut since they're too slow against a deck full of free countermagic and Wasteland. Keep Force of Will, Daze, and Wasteland as the mirror-breakers they are.