An ancient martial art, rumored to have been developed by old Yuan-ti who studied snakes, figuring out how to use ones Ki as a poison to others, and learning how to maximize the effectiveness of grappling. 

Snake Traits

When you take this subclass at level 3, you gain the following benefits

-You can add your Dexterity modifier to any checks made to grapple a creature. You also have advantage on Strength checks made to grapple a creature that is smaller than you. While a creature is grappled by you, you can use your bonus action to restrain the creature. 

-When you hit a creature with Flurry of Blows, you can attempt to inject poisonous Ki into the creatures system. The creature must make a Wisdom save, the DC of which is equal to your Ki save DC, and if the creature fails, it is poisoned until the end of your next turn. This poisoning ignores immunity to the Poisoned condition. You can use this feature equal to your proficiency modifier, and recharges on a long rest. While you have no uses available, you can spend 1 ki point to use this feature again.

-When a creature targets you with an attack, you can use your reaction to cast Sanctuary on yourself by spending 2 ki points, as the creatures mind is filled with the sound of snake rattles. The DC for this spell is equal to your Ki save DC.

Paralyzing Strike

At 6th level, you gain the ability to inject poisonous Ki into a creatures system. When you use the Stunning Strike feature, you can expend an extra Ki point to paralyze the creature you hit instead of stunning them

Improved Snake Traits

-When you use your Flurry of Blows to poison a creature, the creature takes poison damage equal to 2 rolls of your martial arts die on a failed save, and take half damage on a passed save. This poison damage ignores resistance to poison damage, and treats immunity to poison damage as resistance.

-While a creature is grappled and restrained by you, you can perform a crushing attack on them. When you take the Attack action on your turn, the grappled creature must make a Constitution saving throw, the DC of which is equal to 8 + your Strength or Dexterity modifier + your proficiency bonus. On a failed save, the creature takes bludgeoning damage equal to 3 rolls of your martial arts die. 

-When you use ki points to cast Sanctuary, any creature who fails the saving throw becomes frightened of you and must use any movement it has to run away from you.

Lethal Venom

When you use your Paralyzing Strike feature, you can spend 5 ki points to inject a lethal dosage of poisonous ki into the creature. The creature takes 5d10 necrotic damage and 5d10 poison damage, both of which ignore resistances. The ki stays in the system, and can only be removed via Greater Restoration or a Wish spell. While the ki is in the creatures system, it takes 1d10 necrotic and 1d10 poison damage every hour, and it cannot regain hit points. If the ki is not removed within 24 hours, the creature must make a Wisdom saving throw equal to your Ki save DC. If it fails, it loses whatever hit points it has left. If it succeeds, the ki fades from their system