Ditto

Through a combination of Imposter and Choice Scarf, Ditto can turn the tables on a plethora of dangerous setup sweepers, like Barbaracle, Virizion, and Salazzle. Ditto functions well as an offense revenge killer, since after copying one of the opponent's powerful Pokemon, they will usually lack effective switch-ins to it, allowing Ditto to claim one or two KOs before it's forced out. In addition to this, Ditto's ability to refresh its PP indefinitely by switching in and out can be used to PP stall defensive teams, and it can also copy enemy moves as well as utility moves like Heal Bell or Defog for its team's benefit against such teams. However, Ditto does not copy the enemy's HP stat and therefore can only be switched in if predicting an attack that the target Pokemon resists, such as Salazzle's Sludge Bomb, as a pathetic base 48 HP often means it can be severely damaged or outright KOed without good prediction. Despite the move being rather uncommon in RU with the exception of Raikou, Imposter is blocked by Substitute, meaning Ditto can often fail to beat Substitute sweepers. Additionally, Ditto can struggle versus balance, as even if it copies something theoretically dangerous, the enemy team will usually have a sturdy defensive answer. The potential entry hazard stacking nature of these teams can also give Ditto trouble.