PallidPatience said:
An Overrun knocks the opponent prone. Tumble does not. Tumble merely lets you move through an occupied square. They're not really similar at all.
I just thought I'd point that out.
Go back and re-read Overrun.
The target of the Overrun gets to AoO the attacker.
The target of the Overrun can decide to let the attacker move through him.
Tumble Through is identical to Overrun (for moving through, not for knocking down) where the
attacker decides to let the attacker move through the target as opposed to the target making that decision.
In other words, Overrun allows a defense whereas Tumble Through does not. Tumble Through is a superior form of Overrun if your goal is to move through the target (as opposed to knocking him down) because allowing the attacker to move through is taken out of the hands of the defender and put into the hands of the attacker.
The best defender in the world cannot defend against this.
And Tumble Through does not even require the Improved Overrun feat to avoid the AoO. The AoO avoidance is feat free (it just requires skill ranks).
Bottom line: All auto-successes (i.e. high enough skill) where they involve a target and have no defenses are bad rules. Against objects, against situations, sure. Against targets, not so good. Ray spells are like this as well. Even Ray spells which are similar to this (i.e. eventually get to the 95% chance to hit) still have defenses (e.g. miss chances and often spell resistance).
Tumble Through does not have a defense (except for Readied Actions which is a terrible defense). That's a bad rule. Virtually every other combat aspect in the game system has some form of defense.