Your Strength score increases by 2, and your Dexterity and Constitution scores increases by 1.

As a Yuan-Ti Abomination, you stand much higher than Humans around 8-12 Feet tall and more than twice the weight. Your size is Large

Due to your serpentine eyes, you have superior vision in dark and dim conditions. You can see within 60 feet of you as if it were bright light and in darkness as if it were dim light. You can't discern color in Darkness, only shades of gray.

As an action you can polymorph into a Large Snake or back into your true Abomination form. Any equipment you were wearing or carrying isn't transformed. Your statistics are the same in each form. You do not revert back to Abomination form if you die while in snake form.

You can use your long serpent tail to grab or latch onto objects or creatures of Medium size or smaller. You can also use your tail in order to grapple creatures while keeping your hands free. The grapple has disadvantage.

Your snake-like fangs are natural weapons, which you can use when you make an Unarmed Strike. If you hit with it, you deal Piercing Damage equal to 1d6 + your Strength Modifier, instead of Bludgeoning damage with a normal Unarmed strike.

You gain proficiency in the Perception and Stealth skill.

You gain the ability to cast Poison Spray with this trait. You also gain the ability to cast Animal Friendship with this trait. When you cast this spell as part of this trait on a Snake, they have disadvantage on the Saving Throw to resist the spell. When you reach 3rd level you can cast Suggestion with this trait. When you reach 5th Level you can cast Fear with this trait. Charisma is your Spellcasting Ability for these Spells.

You gain immunity to Poison Damage and are immune to the Poisoned Condition.

You have advantage on saving throws against spells and other magical effects. 

You can speak, read and write in Common, Abyssal and Draconic.