Mainboard (60)
This mirror match comes down to who resolves threats first and who can best leverage the discard-madness engine. Searing Blaze comes in to kill opposing Guttersnipes and Kessig Flamebreathers before they snowball damage, since letting those stick is often game-losing. Fireblast is trimmed because the mana flexibility matters less when you need to answer creatures on the board rather than go over the top. Protect your own Guttersnipe and Kessig Flamebreather at all costs — the first player to resolve and keep one of these alive usually wins the game. Highway Robbery and Grab the Prize are key to maintaining card and life advantage in a race that otherwise favors whoever drew more spells.
Dimir Terror is a tempo-control deck that wins by countering your spells, deploying cheap threats like Tolarian Terror and Gurmag Angler, and killing your creatures with Snuff Out and Cast Down. Pyroblast and Red Elemental Blast are essential here — they answer their blue threats and punch through Counterspell to resolve your damage spells. Highway Robbery and Grab the Prize are cut because they're slower card draw sorceries that are poorly positioned against a permission-heavy deck that can counter them before you gain value; your burn suite and Kessig Flamebreather/Guttersnipe engine are the priority. Focus on keeping your spell count high to maximize Kessig Flamebreather and Guttersnipe triggers while using Pyroblast effects to protect key spells and remove their threats.