thanksbulbapedia:

“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 stages of positive Attack stat changes. Also, both of Shuckle’s partners must have the Ability Flower Gift and the weather must be sunny. On the 5th turn of using a Defense Curl-boosted Rollout consecutively without any misses, if used against a level 1 Ledyba with minimum Defense stats, that has 6 stages of negative Defense stat changes (such as from being subject to Screech 3 times), it can deal 481,266,000 damage with a critical hit.”

— http://bulbapedia.bulbagarden.net/wiki/Rollout_%28move%29