On reading all the various thoughts on how overrun works (or doesn't) in conjunction with various feats like Vicious Strike, Spiked Destroyer, Charge Through, etc., I'd like to nail it down in order to present them to my GM when I bring a character in using them.
The Core Rulebook: p201 discusses the Overrun maneuver itself, and here are the feat descriptions:
Imp. Overrun: 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.
Greater Overrun: Benefit: You receive a +2 bonus on checks made to overrun a foe. This bonus stacks with the bonus granted by Improved Overrun. Whenever you overrun opponents, they provoke attacks of opportunity if they are knocked prone by your overrun.
Vicious Stomp: Benefit: Whenever an opponent falls prone adjacent to you, that opponent provokes an attack of opportunity from you. This attack must be an unarmed strike.
Spiked Destroyer: Benefit(s): When you succeed at a bull rush or overrun combat maneuver, you may automatically make an attack roll with your armor spikes against the target of the maneuver as a swift action, using your highest attack bonus.
Charge Through: Benefit: When making a charge, you can attempt to overrun one creature in the path of the charge as a free action. If you successfully overrun that creature, you can complete the charge. If the overrun is unsuccessful, the charge ends in the space directly in front of that creature.
First of all there is the movement up to a target creature I intend to overrun.
1) Can I use Acrobatics to try to avoid any AOO(s) caused by movement up to the target? Why not?
2) If I'm in an adjacent square to my target at the start of my turn, do I provoke an AOO from leaving my square (which normally provokes in any situation except a 5' move or withdraw) in order to attempt to move into the target's space (which also normally provokes)? In other words, does Imp. Overrun only stop the AOO that would normally provoke from attempting to use an untrained overrun, not the move?
3) If I'm using the charge action as part of an overrun, am I getting a +2 attack bonus (and -2AC) to any and all attacks I may make during my turn from things like: the attack roll for the overrun attempt; separate AOO's granted by both Gr. Overrun and Viscious Strike if I cause the target to go prone (CMD+5); a swift action attack using the Spiked Destroyer feat; etc.?
4) I'm pretty sure that I give up the actual melee attack I would normally get at the end of a charge in order to make the overrun attempt. But I've seen people say (mistakenly, I think) that I would still get it at the end of my overrun. But the only way to get that charge melee attack is if using the Charge Through feat in order to get to a second enemy that you continue moving in a straight line towards after overrunning the creature in between your target and where you began your turn.
Now, some questions on what can happen during the overrun itself.
1) Can I even use the Viscious Stomp feat at all in conjunction with an overrun (assuming +5CMD)? Someone is telling me that the AOO won't trigger because the target is falling prone in your same square instead of an "adjacent" one, as the feat requires. However, in the Core rulebook under Combat: Melee Attack, it says, "With a normal melee weapon, you can strike any opponent WITHIN 5 feet. (Opponents within 5 feet are considered adjacent to you.)" I think that says that your own space counts as adjacent, too. It is within 5' of me. Why wouldn't you be able to stomp on someone that falls literally at your feet?
2) Upon the successful overrun with a +5CMD, I think I would get the +4 attack bonus to hit the prone target at my feet with the AOO given with Vicious Stomp since it had to become prone to trigger the AOO. However, the AOO triggered by the +5CMD overrun with Gr. Overrun would not get the prone bonus to the attack since it was triggered by the overrun itself and interrupts before the creature goes prone. As for Spiked Destroyer, it's a swift action, so I'm not sure if it would get the +4 bonus or not. My guess is that it doesn't since it is also triggered by the overrun success, not the target becoming prone.
So, if anyone wants to tackle some or all of this, it would probably help all the others, like me, that are curious about how overrun is meant to work properly. Thanks.
For the first set:
1) I don't see why not, assuming you meet all the requirements outlined under charge and acrobatics
2) I think Imp Overrun only removes the AoO from the target of the Overrun. Movement should provoke as normal.
3) Depends. Technically, action economy precludes Overrun as part of a charge. Obviously, the intention is to allow you do it, because Overrun explicitly says it can be used during a charge. Still, the charge rules themselves only mention giving a bonus to Bullrush. Personally, I allow players to make an Overrun with +2 when charging, but this is really an "Ask your GM" question.
As for other attacks, the rules explicitly award the +2 to the attack at the end of the charge, not as a blanket statement, so it's the only attack that gets +2
If you charged, you have -2 AC until your next turn, period.
4) So Overrun and Charge is weird, as I glossed over above. Using Overrun during a charge shatters the normal charging rules. The action economy is wonky (Overrun is always a Standard Action unless it specifically isn't), and charges have to end in the closest square from which you can attack your target, so you technically can't keep moving into their square, let alone past them. Finally, Overrun doesn't technically replace the charge-ending-attack, so you still have to wind up somewhere you can attack your target, even if you get around the "closest space" clause. At the same time, Overrun was explicitly intended to be used during a charge, but how to make that work, or to even bother to, is up to the individual GM. Personally, I let the Overrun replace the attack and let the Overrunner move past their target, but again, "Ask your GM."
As for the others:
1) Yes. Technically, the square you're in isn't adjacent to you, but any enemies within 5 ft ARE, which includes enemies within your square. Because the feat reads "enemy ... adjacent to you," the rules support stomping them. If it had instead read "enemy ... in a space adjacent to you/yours," I'd say that they're technically safe. I'd still give you your AoOs personally, though. Also, I might be wrong about your own square not being adjacent to you.
2) I don't think Gr Overrun and Vicious Stomp stack, as both are triggered by the opponent going prone. If they do, they should both get the prone attack bonus.
As for Spiked Destroyer, it triggers on the successful Overrun but so does the proning. I think they happen at the same time, so you don't get the bonus there (presumably, you hit him with your spikes at the same time you knock him over).
Thanks, Dallium, for getting back to me. It took me a couple of days to notice.
Can you elaborate a little more on your answer to my 2nd question, please? Let's also assume no other opponents are involved. You're saying the overrun attempt doesn't provoke (due to Imp. Overrun), but the act of leaving my square to move the 5' necessary to enter the opponent's space still provokes from the overrun TARGET. So, no matter how close or far you start, an overrun will pretty much always provoke a movement AOO from your target.
EDIT- I think I see what you mean. The FAQ/Errata for Vicious Stomp mentions that the AOOs provoked by Gr. Trip and VS are not provoked in quite the same way, and thus they both give you an AOO. But Gr. Overrun and VS ARE provoked by the same action (target falling prone adjacent to you), so they would NOT STACK.
It could be argued that Imp Overrun doesn't help with the AoOs one provokes while moving, but I think the wording of the Overrun rolls the actual combat maneuver into the movement in such a way that the movement from Imp Overrun doesn't provoke, as it's part of "performing an overrun combat maneuver." The problem with that interpretation is that movement no longer provokes at all, so a character could use their Imp Overrun to get out of a pack without provoking. At the table, I would probably rule that Imp Overrun just means you don't provoke your target.
Basically, I think you either provoke from everybody or provoke from nobody, and I don't think that's how it was supposed to work.