Nero24200 author of Steel Mountain has given his approval with the following words:
Looks fine to me. Feel free to add it to the class.
EDIT: And so as not to Triple (Quadrupal?) post, here is another discipline: Black Heron:
The Unparalleled Prowess ability for Black Heron:
Keep in mind that this works against summoned elementals and most constructs, vermin, and animals, and not a few magical beasts.Black Heron: When confronted by those whose morals are middle of the road, or those who pursue Evil, but along a path that brings them into conflict with the Black Heron Adept, the strikes are not as powerful. A Master of Black Heron on the other hand, has such conviction in HIS brand of cruelty, sadism, and greed that he treats all targets as good for purposes of determining the amount Unholy damage they take from his maneuvers.
And here is my thought for a Focused Rivalry ability:
I don't know how many sources of Unholy damage their are out their, so I don't know how powerful this is.Black Heron: You take half the unholy damage you would otherwise take. This means that if you are neutral or evil, you will generally take 1/4 the rolled amount.
Also, it occurs to me that "Focused Rivalry" gets a BIT weaker the more disciplines there are, although a lot of the abilities have broader utility than just countering the specific discipline. Given that the idea here is that Adepts are supposed to be really common in this setting, I don't think this is much of a problem for AoW, since even the most obscure disciplines should come up once or twice in a given campaign.
EDIT^2: Also, the Tiger Claw Unrivaled Mastery ability actually penalizes you for having a higher BAB sometimes. "and the other attacks are made at the Master of One's lowest iterative attack bonus." so if you have a +10 you get your second at +5, but if you have a +11 you get your second at +1.