WoWDB

Grants buff of the same name with a duration of 20 seconds and is refreshed whenever you trigger  Mastery: Combo Strikes.  The buff caps at 67 100 stacks for a 134% 100% chance to activate  Invoke Xuen, the White Tiger.  (Yes, I was bored enough to test this.)

Edit: Updated to reflect the January 30th hotfix:

 

• Fury of Xuen can now stack up to 100 times (was 67).
• Developers’ notes: In a hotfix made yesterday, the per-stack percentage went from 1.5 to 1%. We want the total chance to still be able to stack up to 100%.