Dismember is premium removal for Dragon's Rage Channeler and Murktide Regent, killing either cleanly at instant speed. Thorn of Amethyst taxes their cantrip-heavy, noncreature-spell plan (Brainstorm, Ponder, Flow State, Lightning Bolt) and slows down Cori-Steel Cutter's Flurry trigger reliance on cheap spells. Sire of Seven Deaths and some It That Heralds the End copies are too slow against this aggressive tempo deck. Chalice of the Void set to one is excellent here, shutting off their one-mana cantrips and Lightning Bolt.