Hey, Majou. My take on the typhoon kick mastery is that it's fine, I mean, I don't see a problem with it, but I think that the flying kick double damage should not apply to the second attack.
I was looking at your mastery abilities as possible material to use in my own campaign world, and to be honest, I'd use another kicking mastery, but at the same time, I don't see a problem with the one you designed. The prone ending is an interesting drawback, as is the AOO threat. Have you seen a movie or other media that has this technique in it?
For the kicking mastery, the first thing I'd do is allow circle kick to apply to standard attacks, excluding AOOs and flying kick, to modify the existing feat, which requires a full attack action. The second mastery would combine circle kick with flying kick, but apply double damage to the first attack only. As for cleaving, perhaps you could allow an attack within 5ft. as a normal melee kick attack, upon landing after the kick- not sure if that would be a Mastery II or III, or it's own mastery. Come to think of it, a grab bag of masteries might work- not everyone kicks the same, right?
Have you seen the kick technique from DOA2, where the ninja girl leaps feet first and spins like a drill, hitting her target with both feet? She then lands prone, but it looks like she gets up as a free action- even if she misses, she gets on her feet almost instantly. The question is, would that attack constitute a mere flashy flying kick with some power attack added to it, or would it require mastery and special rules? I'd say you'd need at least Acrobatics +10 to pull that off.
BTW, I don't know how to link to the PrC threads on this board. All you have to do to find the Drunken Monk and Mystic Blade is input the names in a search, or perhaps browse House Rules. They're in here somewhere.
And, thanks for the clarification on the grappling AOO. Pretty powerful, but it seems fine, as the martial artist has to be high level to attain it. Grapplers will invest in bonuses to their grappling/trip attack rolls, so it won't be too easy to get the best of the grappler, in any case. I think the grappler should have a mastery that enables him to turn a grappling block into a grappling attempt, without this kind of AOO penalty. The paper-rock-scissor war could go on and on.
