Mono-Blue Terror's maindeck is entirely blue, so Pyroblast and Red Elemental Blast hit nearly everything they play, including Counterspell, Brainstorm, Thought Scour, Mental Note, and even their Tolarian Terror/Cryptic Serpent/Delver of Secrets threats as blue permanents. This lets us protect our burn spells from countermagic while also having a cheap answer to their undercosted threats. Cut slower value cards like Highway Robbery and Melded Moxite since we want maximum interaction and speed to close the game before their card-advantage engine takes over.