Subtly Skilled
Prerequisite
A nightstalker’s true strength isn’t brute force—you are an infiltrator, deceiver, a voice in the right ear or a knife to the right neck, and you turn your physical and mental discipline into the subtlest of manipulations and subterfuge.
You may add your martial arts die as a bonus to Acrobatics, Culture, Deception, Engineering, Intimidation, Investigation, Sleight of Hand, Stealth, Perception, Performance, and Persuasion checks.
Source