Dimir Terror is a tempo-control deck that wins by filling the graveyard quickly to deploy massive threats like Tolarian Terror and Gurmag Angler cheaply, backed by Counterspell and Snuff Out for disruption. Your game plan is to go under them with aggressive one-drops and pump spells before their threats come online — every point of damage counts since they can stabilize quickly with a 5/5. Bring in Pyroblast and Red Elemental Blast to fight through their counterspells and answer Tolarian Terror at instant speed; these are especially valuable since their entire threat suite is blue. Cut Reckless Impulse since it's a sorcery that does nothing proactive on the key early turns and End the Festivities since it's a sideboard card that has no targets here. Keep Rally at the Hornburg as your best way to push through a lethal attack when they have a blocker, and prioritize keeping your mana open on key turns to fire off a Blast when they tap out to deploy a threat.