First off, here are relevant citations for what all of these things do:
Weapon Style Mastery: Lets you combine a Weapon Style with a regular Style.
Ascetic Style: Allows you to apply the benefits of feats with Improved Unarmed Strike as a prerequisite to the selected weapon. A 5th level monk can apply this to any weapon in the monk weapon group.
Street Style: Can only be used in Urban terrain.
Street Carnage: While using Street Style, your unarmed strike critical multiplier is x3.
Am I correct in saying that these all combine to allow a monk to use an urumi (1d8, 18-20/x2, monk weapon group) with a x3 critical multiplier while in urban environments?
Adding in Improved Critical or the keen property for a 1d8, 15-20/x3 weapon sounds a little bit ridiculous, but it seems like this is legal.
EDIT:
I've been playing with this a bit. Even as a human, it doesn't seem terribly viable to get this combo going before about 13th level -- at least not on an Unchained Monk chassis. I think that somewhat blunts the effectiveness, making it far more reasonable.
Considering just how many feats are being pumped into doing it, I don't think it's ridiculous to end up with a highly conditional combat bonus like that. Compare that to just using Ascetic/Dragon to grant weapons used in one hand Dragon Style strength bonuses - even if you're using two of them at the same time.
With a 3 level dip into Weapon Master Fighter, I think you can manage to pull it off by 11 if you get a keen weapon. (If your table allows ways to gain proficiency with exotic weapons other than just taking the feat, you can pull it off by 9.)
Though, here's a question... If you're a monk, does Ascetic Strike actually do anything for you? Ascetic form lets you use class abilities that can be used with an unarmed strike with your chosen weapon. Scaling unarmed strike damage is a class ability that can be used with an unarmed strike. Given that, is there any reason to take Ascetic Strike unless you're not getting that class feature anyway or it's more than 4 levels behind your character level?
There was some talk here about how Ascetic Style was only supposed to work with feats, not unarmed strike damage. Considering Ascetic Strike, I think that was the intent.
Yeah, I've seen the author's intent for Ascetic Style, and for that much, I agree. Ascetic Form, on the other hand, specifically says, "You can use the chosen melee weapon with any class ability that can be used with an unarmed strike, such as an unchained monk's style strike ability."
Yeah, as far as I can tell, Ascetic Form defeats any purpose for Ascetic Strike on an actual Monk.
Oh yeah, reading for the win! Chalk it up as another Prone Shooter feat, I guess.
Well, it does mean a level 11 character using it with Monastic Legacy could grant any Monk weapon a 2d6 die.