Serpent blood

You find yourself as a vessel of deadly poisons and yuan-ti tricks, whether by mutation or heritage. Rogues of this archetype are masters of charm and poison, using their unique traits as a means to kill and deceive. 

Bonus proficiencies

When you choose this archetype at 3rd level, you gain proficiency in deception or persuasion. you also gain proficiency with the poisoner's kit.

Venomous

When you choose this archetype at 3rd level, your body starts to naturally produce a potent venom, you can inject this venom into an enemy as a bonus action an amount of times equal to your proficiency bonus, this resets after a short rest. Alternatively you can produce a vial of injury poison after a short or long rest. this vial can coat one item or 3 pieces of ammunition and can be applied to Weapons, Ammunition, trap Components, and other Objects that deal piercing or slashing damage and remains potent until delivered through a wound or washed off. A creature that takes piercing or slashing damage from an object coated with the poison is exposed to its Effects. When affected by this poison, the target must make a constitution saving throw which DC = 8 + your proficiency modifier + your charisma modifier. on a failed save they take damage equal to your Sneak Attack, on a successful save they take half damage.

Coil

You can spend your bonus action getting into a coiled stance, this stance lasts until the start of your next turn, you cannot enter this stance if you have moved, you cannot move once you enter this stance. all weapon attacks from this stance have advantage. 

Alluring words

By 13th level, you have gotten more in touch with your yuan-ti side. You can cast suggestion an amount of times equal to half of your proficiency bonus rounded down. The DC = 8 + your proficiency bonus + your charisma modifier.

This ability resets after a long rest.

Vanish from sight

When you reach 17th level, you have become attuned to your psychic power, able to manipulate creatures minds. Whenever you hit an creature with a sneak attack, you can convert your weapon damage to psychic damage and vanish from the enemy's sight, being treat as an invisible creature to them until the start of your next turn.