Your Ophidian Affinity is Better than most in the Pureblood Caste you have the Capability to Transform into a Snake just like a Yuan-ti of a Higher Caste

As an action you may Polymorph yourself into a Medium Giant Poisonous Snake, Or a Large Constricter Snake. Your statistics are the same in each form except for the size change noted. Any Equipment your wearing or Carrying isn't transformed. And you do not change forms if you die.