This new rogue archetype is a straight-up adapatation of the Master of the Scaled prestige class from the previous edition.

Mechanically, it is a variant of the Arcane Trickster subclass from the PHB. In particular, it gains spells much faster than the Arcane Trickster (as fast as a paladin or ranger), thus reproducing the spell progression from the 3.5 prestige class. This seems slightly unbalanced, and perhaps a slower sneak attack progression (as in the original prestige class) would compensate. The Fast Talker class feature seems also very powerful in a social context, and I would limit it more (either recharging in a long rest or by forcing the expenditure of spell slots to activate it).

Otherwise, it works pretty well and fits the Scarred Lands mythos perfectly.