Lead with entry hazards (Stealth Rock/Spikes) to break Focus Sashes immediately.
Moves like Encore (learned by choice encounters like Poliwag or Togekiss) completely break the AI. If a trainer uses a non-damaging setup move, lock them into it with Encore, then switch to a setup sweeper to win the battle immediately. End-Game Preparation: The Elite Four Prep sacred gold nuzlocke tips updated