Gaddock Teeg is very strong against WU. It stops their four Force of Will outright, since a mana value 5 noncreature spell can't be cast even for its alternative cost. After sideboarding it also stops Wrath of the Skies and Prismatic Ending, which have {X} in their costs. It leaves their Phelia and Tamiyo creature plan untouched, and it does not stop Teferi, Time Raveler, which is only mana value 3. Be aware that Teeg also stops our own Green Sun's Zenith while it is on the battlefield. Swords to Plowshares is a clean, cheap answer to Phelia, Tamiyo and Quantum Riddler, and Endurance is a sturdy flash body with reach that holds off Tamiyo. Force of Vigor stays in the sideboard, because their deck has almost no artifacts or enchantments to hit. Outland Liberator and Shadowspear aren't doing enough against a deck with so few artifacts and enchantments to target and no need for lifelink pressure. Sylvan Safekeeper is lower impact because every activation costs a land against a deck with four Wasteland.