Well, first you take a pokemon that knows Beat Up but make sure it won't do much damage to the next pokemon.(LikeWhimsicott) Then you take a Terrakion as the next pokemon. Whimsicott uses Beat Up on Terrakion. Since Whimsicott has low attack, it won't do much, but thanks to Terrakion's Justified, each hit from Beat Up would raise Terrakion's Attack 2,4, 6 times! That would make Terrakion from a physical sweeper to a phyical MURDERER!