Beat Up differs significantly from almost all other moves in the game. While it is a damage-causing move, how it does so is unlike any other move. The differences are as follows.
First off, the damage for Beat Up is not calculated only from the pokemon who uses the move and the target. The damage calculation is run for each pokemon on the using pokemon's team and the results are added together to get the total damage for the attack. There is a limiting factor for which members of the team for which the calculation can be run. Any pokemon that has one of the conditions that affect the status monitor will not be a part of the damage calculation. This includes pokemon that are Asleep (SLP), Frozen (FRZ), Paralyzed (PAR), Poisoned (PSN), or, the big one, Fainted (FNT). In other words, if you have a 6 member team with 3 of the other pokemon paralyzed and 1 fainted, only 1 of the other pokemon will be adding their damage to the calculation.
Next is the fact that Beat Up is an effectively-typeless attack. Like Future Sight and Struggle, the damage from Beat Up will be neither increased nor decreased based upon the type(s) of the pokemon involved. This typelessness extends so far as to ignore that Dark attacks are Special-based. Attack and Defense are used instead of Special Attack and Defense.
The most unusual feature of Beat Up is that it does not use the Attack and Defense stats of an individual pokemon in the appropriate areas of the damage formula. Instead, Beat Up uses the base Attack and Defense values for the species of the pokemon involved. Nothing else modifies these values during this calculation. This includes things that are always included (such as DVs and stat experience) and things that are sometimes included (stat modifiers such as Swords Dance, Barrier, etc.)
Beat Up receives the flinching bonus when King's Rock is attached to the using pokémon.
Beat Up is affected by Brightpowder when the opposing pokémon is equipped with it.
