Beat Up inflicts damage on the target, with one strike for each conscious Pokémon in the user's party that does not have a non-volatile status.
Beat Up ignores changes to stat levels such as Swords Dance, but each strike does increase in power from Attack-boosting items like the Choice Band if held by the user.
If a Focus Sash, Focus Band, or Run Away activates before the last strike is dealt, the following strike will cause the defending Pokémon to faint.
Each strike has an independent chance of being a critical hit, as well as activating a King's Rock or Razor Fang or the ability Stench. The Sniper ability does not affect critical hits. Bide and Counter deal damage based on the last strike alone. A Focus Band can still activate repeatedly to prevent fainting, but each chance is independent.
If a Pokémon uses Beat Up on its partner in a double battle, the partner will attack itself (unless it suffers from a status ailment).