Dimir Control leans on Counterspell, Snuff Out, and a suite of small tempo creatures like Faerie Seer and Spellstutter Sprite, so Pyroblast is live to counter or destroy their blue spells and creatures on the way in. Their sideboard also brings Sewer-veillance Cam, a small flash artifact, giving Annul a marginal but real target. This matchup is a grindy attrition fight, so keep your card advantage engines like Lorien Revealed and Brainstorm in and simply trim the weakest cards, Pulse of Murasa and Campfire, for more interaction. Watch out for Snuff Out, which can be cast for free off 4 life against your key threats like Murmuring Mystic.