So I'm playing a Weretouched Shifter/Alchemist and wanted to check some thing.
If I take Vestigial Arm, does that remain when I assume my hybrid form? Or does it disappear?
Ask yourself this question; "Would a creature with X form gain Y feature if it took levels in Z class."
If yes, it is a class feature not dependent on physical form.
You also lose any class features that depend upon form, but those that allow you to add features (such as sorcerers that can grow claws) still function.
The Vestigial Arm discovery adds a feature. You get to keep it while polymorphed.
Alternatively, if you had a class feature that allowed you to constrict with your serpentine body and polymorphed into a biped, you would loose the ability to constrict.
Just found this in the Bestiary on Monstrous Lycanthrope
"A monstrous lycanthrope can take any of three forms: the base creature’s form (called normal form), a hybrid form, or the werecreature’s form (called monster form). The hybrid form has the normal form’s body shape and number of limbs and heads, but it shares certain characteristics of the monster form, including scales, fur, and skin tone. The hybrid form might also include smaller versions of the monster form’s wings, horns, or facial features, or even vestigial limbs (or heads) of the monster form that the normal form does not possess."
Would that apply to me?
You are not a monstrous lycanthrope, or even a lycanthrope at all. You are a (insert race here) weretouched shifter/alchemist.
AFAIK, "monstrous lycanthrope" isn't even a thing outside of third party.
Sorry, I was referring more to the bit about how the hybrid form keeps limbs of the normal form
If you're talking about the "monstrous lycanthrope" on d20pfsrd, that's from a third-party product and has no bearing on interpreting first-party rules.