UB relies on Dark Ritual and cantrips (Brainstorm, Ponder, Mishra's Bauble) to power out Stormchaser's Talent and protect with Force of Will and Daze, so Disruptor Flute is your best sideboard card, taxing nearly every spell in their deck. Damping Sphere compounds this by limiting the burst mana from Dark Ritual and Lotus Petal. Soul-Guide Lantern strips their graveyard value from Flow State and any Barrowgoyf-adjacent plans they bring in. Their graveyard plan is minor, so Grafdigger's Cage and Bojuka Bog are cuttable along with Karakas and the Icetill Explorers to fit the full taxing package.