UBG is a reanimator deck relying on Reanimate, Animate Dead, and Shallow Grave to cheat Atraxa, Griselbrand, or Archon of Cruelty into play, so Endurance flashing in for free (by exiling a green card) to put their graveyard on the bottom of their library is a huge blowout against their discard-a-fatty plan. Our existing Grafdigger's Cage already stops creature cards in graveyards from entering the battlefield, which shuts off their Reanimate/Shallow Grave/Animate Dead lines entirely, so Endurance gives us extra redundancy against that plan. Trim Disruptor Flute since it is too narrow against a deck with many different enablers rather than one choke point.