UB Reanimator wants to Reanimate or Animate Dead a Griselbrand or Archon of Cruelty, or cheat Atraxa in via Shallow Grave. Teferi, Time Raveler's static ability forces them to cast spells only at sorcery speed, shutting off instant-speed Shallow Grave and Dark Ritual tricks at the wrong time, while Teferi's minus ability can bounce a reanimated threat back to hand. Prismatic Ending can exile cheap permanents like Animate Dead (mana value 2), which takes the reanimated creature with it, or a Lotus Petal. Omniscience is too slow against their fast reanimation plan and gets discarded by Thoughtseize before we can use it, and Stock Up is too slow to dig with, so both are cut for proactive interaction. Veil of Summer stays in because it gives us hexproof from black, which blanks Thoughtseize, Unmask, and Cabal Therapy aimed at us, and it keeps our spells from being countered. Race to assemble Aluren or hold up interaction like Force of Will to stop them before they reanimate a game-ending threat.