UB is a cantrip-and-disruption deck similar to Dimir Tempo, using Thoughtseize and Force of Will to protect its plan while pressuring with Stormchaser's Talent and The Fantasticar, so Thoughtseize is key to strip their interaction or a threat before you commit to combo. Mindbreak Trap answers Force of Will/Daze protecting their own game plan and lets your win condition resolve cleanly. Hexing Squelcher's tax rarely matters against a low-curve, cantrip-heavy deck, so it's cut for more proactive disruption, and Cabal Ritual is trimmed since disrupting their hand is more valuable than extra mana in this interaction-heavy matchup. Sequence Thoughtseize before your combo turn whenever possible to clear a path for Tendrils of Agony or Song of Creation.