A creature can aid an ally’s attack against an enemy. This action represents a feint, a distraction, or some other action that makes it easier for the ally to hit the enemy.
Aid an Ally’s Attack
Action: Standard action. When a creature takes this action, it chooses an enemy adjacent to it.
Grant Bonus to Attack Roll: The creature chooses an ally. That ally gains a +2 bonus to its next attack roll against the chosen enemy. This bonus ends if it is not used by the end of the aiding creature’s next turn. A creature can take the aid attack action only once to affect a particular attack roll. However, up to four creatures can take the action to affect the same attack roll.
Published in Rules Compendium, page(s) 237.