Shuckle

"A level 100 Shuckle can potentially deal the most damage in one single attack through the use of numerous stat boosters; by receiving the effects of Helping Hand from two allies in a triple battle, holding a Metronome, Power Trick, a Skill Swap to Pure Power, and 6 Attack boosts. Also, Shuckle's partner must have the Ability Flower Gift and the weather must be sunny. On the 5th turn of using Rollout consecutively without any misses, if used against a level 1 Ledyba, Yanma or Combee with minimum Defense stats, that have been hit with negative Defense modifiers (such as Screech), it can deal 320,844,024 damage with a critical hit."

- Bulbapedia <bulbapedia.bulbagarden.net/wiki/Shuckle#Trivia>

The 5th use of the rollout has to be from mimic... then max damage, as far as I know. Otherwise correct.