Re: Ideas for a "snake-themed" half villainess
I imagine that some of the "abilities" you want the character to have will be largely informed by what backdrop you are thinking of. In various cultures, snakes have a wide array of mystic importance. Some are life givers, some marked by evil, and everything in between. But moving on from that, somethings that I tend to like when I create snake based characters are:
"Skin Shedding" - Shapeshift into any human or snake form.
This also gives you the ability to fit into small spaces because the S.S. allows you to change your size by up to 15%. Add that with the "touch" group shapeshift and contortionist, you can reasonably fit into small spaces.
"Venom" - Various bite attacks built with a standard poison construct.
"Snake Senses" - Enhanced senses.
The suite of senses would be things like: Targeting with smell, Ranged through touch (Ground vibrations / Air movements), maybe heat vision
"Snakes Guile" - Striking Appearance
"Snake Dance" - Mind Control
"Summon Snakes" - Summon snakes.
Various Skills, etc.
As to Martial arts, though, unless I'm building an actual Martial Artist, I leave that stuff off. In the cases where I have built in Martial Arts, I have done with by having a "multiform" for the Snake and human. The Snake would be the personification of of their "true" self and would have various grabs, etc., but not actually be defined as being a specific "style".
Hope that helps.