When you reduce an enemy to 0 hit points, you gain 9 temporary hit points. Due to your pact with the serpent god Sseth, you have this ability. 

Your Charisma score increases by 2, and your and Intelligence modifier increases by 1. 

Yuan-ti are a little bulkier and taller than humans. Your size is medium

Your fangs are natural weapons, which you can use to make unarmed strikes. If you hit with them, you can deal piercing damage equal to 1d6 + your Strength modifier. instead of the bludgeoning damage normal for an unarmed strike. 

You gain proficiency with two of the following skills of your choice: Arcana, History, Insight, Religion, and Survival.

You have made a pact with either Dendar The Night Serpent or Sseth and they have bestowed upon you these abilities

You can use your action to polymorph into a Medium snake or back into your true form. Your statistics are the same in each form. Any equipment you are wearing or carrying isn't transformed. If you die, you stay in your current form.