In melee combat, you can help a friend attack or defend by distracting or interfering with an opponent. If you’re in position to make a melee attack on an opponent that is engaging a friend in melee combat, you can attempt to aid your friend as a standard action. You make an attack roll against AC 10. If you succeed, your friend gains either a +2 bonus on his next attack roll against that opponent or a +2 bonus to AC against that opponent’s next attack (your choice), as long as that attack comes before the beginning of your next turn. Multiple characters can aid the same friend, and similar bonuses stack.
You can also use this standard action to help a friend in other ways, such as when he is affected by a spell, or to assist another character’s skill check.
You may assist an ally within reach against a common enemy. As a move action, designate an ally within your melee reach that is currently being threatened by an enemy's melee reach (but see below), make an attack roll against an AC 10. If you succeed you grant that ally a +2 bonus that lasts for a short time. That ally can, until the beginning of your next turn, choose to apply that bonus to his AC against the next attack that enemy makes against him, to his next attack roll against that enemy, to an opposed ability score check, or to his next Reflex saving throw made to avoid an effect that enemy produces. The ally must be able to see or hear you (no skill check necessary unless you are trying to remain hidden/unheard, in which case you must also succeed on a Hide or Move Silently check opposed by that ally's Spot or Listen check respectively).
At your option, you may instead make the attack roll against an AC of 15 to increase the bonus to +3, or AC 25 to increase it to +4. If you do, and the attack roll fails to hit the target AC, your ally gains no bonus. Using the aid another action never provokes an attack of opportunity. Multiple aid another bonuses stack, but you cannot aid the same ally more than once per turn (if you can take multiple turns in the same round you could potentially give the same ally multiple aid another bonuses).
You can make a bull rush as a standard action (an attack) or as part of a charge. When you make a bull rush, you attempt to push an opponent straight back instead of damaging him. You can only bull rush an opponent who is one size category larger than you, the same size, or smaller.
Initiating a Bull Rush
First, you move into the defender’s space. Doing this provokes an attack of opportunity from each opponent that threatens you, including the defender. (If you have the Improved Bull Rush feat, you don’t provoke an attack of opportunity from the defender.) Any attack of opportunity made by anyone other than the defender against you during a bull rush has a 25% chance of accidentally targeting the defender instead, and any attack of opportunity by anyone other than you against the defender likewise has a 25% chance of accidentally targeting you. (When someone makes an attack of opportunity, make the attack roll and then roll to see whether the attack went astray.)
Second, you and the defender make opposed Strength checks. You each add a +4 bonus for each size category you are larger than Medium or a -4 penalty for each size category you are smaller than Medium. You get a +2 bonus if you are charging. The defender gets a +4 bonus if he has more than two legs or is otherwise exceptionally stable.
Bull Rush Results
If you beat the defender’s Strength check result, you push him back 5 feet. If you wish to move with the defender, you can push him back an additional 5 feet for each 5 points by which your check result is greater than the defender’s check result. You can’t, however, exceed your normal movement limit. (Note: The defender provokes attacks of opportunity if he is moved. So do you, if you move with him. The two of you do not provoke attacks of opportunity from each other, however.)
If you fail to beat the defender’s Strength check result, you move 5 feet straight back to where you were before you moved into his space. If that space is occupied, you fall prone in that space.
You may force an enemy to move, pushing him in any direction if you are strong enough. As a standard action, you may enter an adjacent opponent's space and force him to move a minimum of 5ft by making an opposed Strength check. Entering the opponent's (henceforth referred to as the defender) space provokes an attack of opportunity from each enemy threatening you, including the defender, however any attacks not made by the defender have a 25% chance of targeting the defender (roll for this chance before taking the attacks of opportunity). Attacks of opportunity cannot interrupt the bull rush even if the attack renders you unconscious or dying; your momentum allows the bull rush to resolve normally.
After the attacks of opportunity are resolved, make an opposed Strength check against the defender. If you or the defender are of different size categories then the combatants gain a size modifier on their respective checks (if both you and the defender are the same size category neither of you may add a size modifier, see the grapple rules for rules on size modifiers). If you succeed, the defender is forced to move 5ft away from you (that is, after the bull rush action is resolved he must be at least 5ft away from you). If you fail, the enemy pushes you back into the space you started the bull rush from, and the enemy does not move.
If you beat the defender's Strength check by 5 or more points you may move the defender an additional 5ft; this is cumulative, so beating the defender's check by 20 means you could push him a total of 25ft. At your option, you may pursue the defender's forced movement as part of the bull rush. You may only move up to your speed, if your base land speed is 20ft you can only pursue the defender for 20 of movement, but if you had a fly speed of 50ft you could pursue him for 50ft, and you cannot move further than how far you forced the defender to move (so even if you have a 50ft fly speed you'd have to beat the defender's Strength check by 45 to move that full speed). The movement used to enter the defender's space does not count against this movement. You do not need to follow the same path as the defender, but you must end your movement adjacent to the defender if you choose to pursue him. You may choose not to pursue the defender, and doing so has no effect on the bull rush's outcome.
Even if you successfully bull rush the defender you cannot change the direction of the bull rush once you've picked it; all movement from the defender must be in a straight line. If the defender cannot move far enough to go the full distance the bull rush would require, if the movement is blocked by a wall or an exceptionally larger creature for example, the defender falls prone in the furthest space he could move to and takes damage equal to your Strength modifier. The defender's movement provokes attacks of opportunity from other enemies threatening him, including enemies he is forced to move past, but not from you. If you chose to pursue him you do not provoke attacks of opportunity for doing so.
You may also use a bull rush action as part of a charge action. After resolving the normal attack (or attacks, if you can make multiple attacks on a charge) from the charge, you enter the opponent's space and make a bull rush attempt with an additional +2 bonus on the Strength check. If you succeed, resolve the bull rush as above, you cannot pursue the opponent. You may attempt the bull rush even if the charge action's attack missed, but only if you could enter the defender's space. If, during the charge action, you don't have enough movement to enter the opponent's space you cannot attempt a bull rush with that action. Attempting a bull rush as part of a charge doesn't require any additional actions; it's part of the same full round action you initiated the charge action with. A bull rush made as part of a charge doesn't provoke additional attacks of opportunity, even from the defender (the charge may still provoke attacks of opportunity however).
So, thoughts on these changes? I was aiming to make them more useful/powerful (namely changing up the AoOs on Bull Rushing and making Aid Another significantly easier), but want some outside opinions on the subject.