Preliminary Comments: I believe the withdraw action is flawed and a better way of avoiding AOOs (without using acrobatics) is called for. The problem I see is that one can take a 5’ step and then cast a spell or make an attack or any other standard or full-round action. But if you move that same 5’ and then move further, suddenly you provoke an AOO. The only way to avoid this is to use the withdraw action, which limits you to movement. What I don’t get is why after getting clear of the threatened square the rules should limit you so severely for movement but not at all for the 5’ step.
My concern is supported by the fact that the rules allow you to avoid AOOs using the acrobatics check and the only penalty invoked is half-movement through the threatened squares. So what follows is my proposed house rule to provide a more consistent way to avoid AOOs without using acrobatics or withdraw.
As I see it, the withdraw action allows avoiding the AOO for the first square moved out of because the character is choosing his moment to withdraw when the opponent is unable to make an AOO (perhaps because he is busy attacking someone else or dealing with another threat or threatening someone else). I reason this mainly requires time and the way to pay for time is to sacrifice movement. Since withdrawing from a threatened square is movement, it seems reasonable to make it cost movement and after that cost is paid, let the character move further if he has any movement left, just as happens when using acrobatics to avoid an AOO.
A simplified version of this has been play-tested and works well. Some of the players had previously complained about the rules for AOOs, and this rule helped them cope by giving them an option to avoid the AOO when they did not have high acrobatics skill and did not want to forfeit a standard action to make the move using the withdraw action or when they wanted to move through a threatened square part-way through a move action.
House Rule: Cautious Movement (replaces Withdraw)
A Cautious Move action mirrors a normal move action in that it can be done as the move action of the round and it can also be done in place of a standard action (a double move). When using the Cautious Move action, however, a character may not do any of the things that a move action allows one to do while moving, such as draw or sheath a weapon, make an attack using the Spring Attack feat, etc.
When making a Cautious Move, any movement that would provoke an AOO for moving out of a threatened square can be made without provoking the AOO by using up a set amount of movement related to the CMD of the opponent who threatens the square you are moving out of. You are watching the opponent and moving at an opportune moment when he is temporarily committed to other activities. If you don’t have enough movement left you may either end your movement in the threatened square or extend the Cautious Move action to a Double Cautious Move to get more movement. [Note: unlike Withdraw, the threatened square you move out of need not be the first square and you can move through multiple threatened squares in the same Cautious Move provided you have enough movement.]
The cost of avoiding the AOO is always at least 10’ of movement. This means the movement out of the threatened square uses a minimum of 15’ of movement. The cost of avoiding the AOO increases to 15’ if the CMD of the opponent is 20-29 and 20’ if the CMD is 30 or more. If the square you move into is not threatened, you may continue moving up to the normal limit of your movement available. There is no limit to the number of threatened squares you can move through in this way except your movement allotment. [So moving through threatened squares becomes like moving through difficult terrain.]
If the square you are moving out of is threatened by two or more opponents, the movement cost from each opponent stacks.
As with the acrobatics option, once you have paid the movement cost to avoid one AOO from a particular opponent, you may move through other squares threatened by the same opponent without provoking an AOO or paying the movement cost or making an acrobatics check.
You may avoid an AOO with an acrobatics check during the same round that you use the Cautious Move rules to avoid a different AOO, if you have the movement. If two or more opponents threaten the same square, you must either use acrobatics to avoid AOOs from both or pay the movement cost to avoid both; you cannot combine acrobatics and paying movement costs to avoid different AOOs associated with moving out of the same square.
If there are also penalties for movement such as difficult terrain, these must be paid as well. The penalties for double or triple movement costs are applied to the actual distance moved before adding the cost for avoiding the AOO(s). If a character does not have enough movement to pay all costs associated with the move, he may not use Cautious Move.
There is no way to use the mechanics of the Cautious Move to move through an opponent’s square. You could use acrobatics to make such a move and use the Cautious Move rules to move out of other threatened squares if you have the movement.
A character can use the Cautious Move to crawl from a threatened square without provoking an AOO but only as a full round action.
A Cautious Move may be made during a surprise round or when staggered, in which case the option to double move is not available.
The way it reads, your proposed variant rule is extremely over-complicated.
The whole point of the withdraw action is to sacrifice your actions to run away. While I agree that not everyone should have to tumble just to get out of a threatened area, I do still agree that you should have to sack your ability to make attacks during a round in order to move to safety.
Here's what I propose (bold italics = edits/additions):
Withdraw
Withdrawing from melee combat is a full-round action. When you withdraw, you can move up to double your speed. The square you start out in is not considered threatened by any opponent you can see, and therefore visible enemies do not get attacks of opportunity against you when you move from that square. Invisible enemies still get attacks of opportunity against you, and you can't withdraw from combat if you're blinded. You can't take a 5-foot step during the same round in which you withdraw.If, during the process of withdrawing, you move out of a threatened square (other than the one you started in), that square counts as 2 squares of movement if you wish to avoid attacks of opportunity from enemies you can see. If you are moving diagonally, moving out of a threatened square counts as 3 squares of movement instead. If you do not have a sufficient number of squares of movement remaining to safely leave a threatened square, moving from that square provokes attacks of opportunity from your enemies as normal.
You may not withdraw using a form of movement for which you don't have a listed speed. You may withdraw while prone, crawling up to 10 feet (essentially spending two move actions to crawl).
Note that despite the name of this action, you don't actually have to leave combat entirely.
Restricted Withdraw: If you are limited to taking only a standard action each round you can withdraw as a standard action. In this case, you may move up to your speed, or crawl 5 feet.
This pretty much encapsulates everything you were trying to do above with half the wording, and still allows you to use acrobatics to tumble if you think there is an invisible attacker nearby, or you just want to tumble to be sure that your last square of movement doesn't provoke, or just to be a cool tumblin' fool.
If you were dead-set on factoring an opponent's CMD into the mix, than I would call for a Reflex save against any threatening creature's CMD, using the same rules and modifiers as Acrobatics to tumble, as everyone has a Reflex save, but not everyone is trained in Acrobatics. This mechanic, however, would become very cumbersome if every character was doing it though (tons of rolls), where as only a few people usually make Acrobatics checks to tumble.
Thanks for the input.
I'd be open to a wide range of ideas about how to achieve the same goal with different mechanics. The thing I think is essential is to give players without a good acrobatics skill bonus an alternative to tumbling to avoid AOOs short of giving up all actions for a full round. Tumbling only costs an extra square of movement and it has the chance of failing, but you don't give up any actions. I'm assuming that the withdraw action works without resorting to acrobatics because the mover waits for the opportune moment to move. I don't see why that should affect anything but how far you can move.
My motive for developing this is: if someone can tumble past an enemy's threat of AOO, why not let someone move cautiously to achieve the same goal? Since tumbling costs you an extra 5' of movement for each normal square, my idea is to make sure it costs someone moving cautiously at least 10' of movement. The trade-off is less movement but guaranteed success.
The simplest version would be to just say it costs 10' extra feet of movement and leave it at that. My adding of the CMD attempts to make a cautious move avoidance of AOO get more difficult as the CMD of the enemy gets higher, just as using acrobatics gets harder when tumbling past enemies with high CMD. And my way is certainly less complicated than acrobatics, which requires you know the exact CMD for each opponent and make a roll. But if you want simpler, make it a set 10' movement cost per threatening enemy.
Likewise, if multiple enemies threatened the same square, it should be harder and in some cases impossible to avoid AOOs just by being cautious. While this rule is wordy, it's straightforward to moderate and only rarely will it be more than a moment to calculate.
The way I see it is that Acrobatics allows you to move and avoid AoOs and then still be able to perform a standard action because there is risk of failure involved and because you have to invest ranks in Acrobatics to do it well. Risk & Investment vs. Reward.
By allowing someone to move unthreatened without any skill, feat, or class investment, and then still be able to attack, has to have a heavier balancer than just less movement. You are comparing a highly skilled and mobile person (Acrobatics) to a unskilled and/or heavily armored person. The consequence for timing your movement to avoid AoOs has to be that you lose the ability to attack after the move.
There are feats and class abilities that let you move and attack without provoking AoO, meaning that there has to be some kind of investment to make it mechanically balanced.
And I guess the CMD thing kind of makes sense, but why doesn't a character's own CMB or CMD (combat skill) play into that equation, only the opponents? Now things are just starting to get complicated.
I prefer Sellsword's system largely because it's a lot simpler. I'd also not want to invalidate Acrobatics any more than it is already; skills are weak enough as it is. And Mobility isn't exactly a must-have feat (actually, I don't remember seeing it in any of the optimisation threads).
That said, Sellsword's rule is effectively saying that anyone can tumble with 100% efficiency if they don't attack, but doesn't let Acrobatics help at all unless they want to attack or move at full speed. Doesn't feel right.
I'm not convinced that the blocker's CMD need come into it at all. After all, the blocker is attacking, not defending. Obviously, this is just a holdover from the Acrobatics rules, but it doesn't work well there either.