Dismember cheaply answers Tamiyo, Inquisitive Student, Phelia, Exuberant Shepherd, and Snapcaster Mage, and the Phyrexian mana means it can be cast through Wasteland pressure by paying life. It does not kill Quantum Riddler on its own: that is a 4/6, and -5/-5 leaves it a -1/1, so plan to remove it with Kozilek's Command or by racing. Null Rod stays in the sideboard. WU has almost no artifacts to hit beyond Clue tokens, and it would shut off our own Lotus Petal. Sire of Seven Deaths and one It That Heralds the End come out because they are expensive, colorless spells that are easy targets for Force of Will, Daze, and Consign to Memory, and they are slow against a deck that can tempo us with Wasteland. Keep Chalice of the Void in to punish their one-mana spells such as Brainstorm, Ponder, Swords to Plowshares, and Stifle.