Alright, so i have a friend who through oversight of product is trying to make overrun the most overpowered combat maneuver. If you look at just the Improved Overrun feat you can see a tremendous difference between it and other maneuvers.
Improved Overrun (Combat)
You are skilled at running down your foes.
Prerequisite: Str 13, Power Attack, base attack bonus +1.
Benefit: You do not provoke an attack of opportunity when performing an overrun combat maneuver. In addition, you receive a +2 bonus on checks made to overrun a foe. You also receive a +2 bonus to your Combat Maneuver Defense whenever an opponent tries to overrun you. Targets of your overrun attempt may not chose to avoid you.
Normal: You provoke an attack of opportunity when performing an overrun combat maneuver.
Sure it gives all the standard things of a Improved feat, the major thing is that last part. You might say making it so they can't just move out of the way is what makes it a viable maneuver at all, but at the same time you have to remember that if they reach +5 the target number it knocks them prone. That alone makes it better then most combat maneuvers, as if you use it as a standard action as part of a move, then you have combined effectively trip and Spring Attack(Something that takes 3 Feat total to achieve) all the while ignoring the movement restrictions of Spring Attack and the attacks of opportunity granted by that movement( at least from the intended target) as well.
That in itself wouldn't be the end all if more things didn't exist to boost it. Greater Overrun makes it provoke attacks of opportunity when knocked prone, again a essentially just greater trip but at the same time it is better since while multi-legged creatures get bonuses against overrun and trip, there are only a handful that can't be knocked prone while there are many more that state they can't be tripped.
The truly overpowered thing about it are if you make a barbarian using it.
Overbearing Advance (Ex): While raging, the barbarian inflicts damage equal to her Strength bonus whenever she succeeds at an overrun combat maneuver.
This makes it even better then trip since it now provides movement, knocks them prone, and afterwords deals damage. At this point the only thing trip has on it is that it can be used during a attack of opportunity or weirdly against flying creatures. That last part being said, with a variety of magic items, a arcane caster, or a potion, they can now fly through them and overrun them since it would still be part of their movement. The final nail in the coffin is a second rage power.
Overbearing Onslaught (Ex): While raging, the barbarian may overrun more than one target per round, with a –2 penalty on her CMB for each overrun check after the first. A barbarian must have the overbearing advance rage power to select this rage power. A barbarian must be at least 6th level to select this rage power.
Sure it is reduced by two for each one after the first, but that potentially allows you in a maximized scenario to hit 8 opponents with it in a turn, more if you have haste or some other movement booster. While a situation like that is fairly unlikely, the bigger concern is a single target. Because of how it is written, their is nothing stopping it other then poor roles from overruning a creature multiple times. Since my friend is based entirely around using this maneuver he plans to have a ridiculous CMB for it (+5 Base Strength, + 4 Rage Bonus, + 2 Improved Overrun, +2 Greater Overrun, + 4 Enhancement Bonus from Belt, + 2 Gauntlets of Skilled Maneuver) at around 7th level he will have a + 25 to his CMB to overrun that will only go up as they level. In a optimal situation against a single humanoid where he is hasted which at 7th level is fairly easy to do as well as being next to them, which isn't to hard to imagine given a lot of monster or NPC written tactics, they can overrun them 7 times at max(1. 5 feet to move onto square and overrun. 2. 5 feet to move off opponent. 3. Repeat 1 and 2 until out of movement). That's potentially 7 * 13(5 Base Strength+ 4 Rage Strength +4 Enhancement Bonus) so 91 damage, plus one attack of opportunity after knocking it down the first time. While i know the chances of getting all those is unlikely, at the same time that is on par with a completely damage specked fighter or Barbarian full attacking while at the same time having a better chance to hit, as the fighter or Barbarian (assuming 2-handed weapon) will be hitting for a average of 34 damage per hit(+ 5 Strength, + 4 Rage, + 4 Enhancement, +2 Weapon, + 6 for 1.5 Strength damage bonus for 2 handed weapon, + 6 for power Attack, +7 Average damage of Great Sword) which assuming they hit with all 3 attacks at 7th level and have haste they will be doing 102 damage, with a potential for a critical hit in there. Just through sheer number of times they would have to roll would make a overrun more likely to fail at one point during the seven attacks, that being said they would more likely average around 4, still 52 damage and knowing the math could decided to call it quits once hitting that number and moving 10 feet away from the opponent, making it impossible for the opponent to attack back, seeing as they would spend a move action to stand up from prone and then another one just to get to them.
Sorry for the long post but mostly putting this out here since I frequently have to GM for them, and short of having something with Reach trip him before he gets to them is there any ways to stop this with normal melee combat? I know spells can potentially shut him down, but the other people we play with know his game breaking potential and will save their rerolls and let him use them for that will or reflex save from anything that might stop him. Only other thing i can think of is that since he's raging he wouldn't have the mental capacity to use it in the ways i described.