Pre-requisites:

By performing rituals a Yuan-Ti Pureblood who has the Yuan-Ti Transformation (Stage One) feat may further transform towards a more snakelike version of Yuan-Ti. In doing so the Yuan-Ti enhances its snakelike abilities. If the Yuan-Ti accentuates these features they are more acceptable to all Yuan-Ti communities.

Melee Bite Attack

To hit = Dex + Proficiency bonus

Reach = 10 ft.

Damage = 1d6 magical piercing damage + 1d8 poison damage (no save).  

Maximum Frequency =Twice per turn. As a bonus action a bite may be used in lieu of an off hand weapon to strike again as part of the same attack (in the same way that 2 weapon fighting allows 2 attacks with an off hand). No free hand is needed in order to make a bite attack. 

Poison Spit Attack

To hit = Dex + proficiency bonus

Reach = 30 ft 

Damage: 2d6 poison damage (no save). 

Notes:

Sneak attack damage, that would normally apply, can be added on top of the Bite Attack or Poison Spit Attack.

Rituals have imbued the Yuan-Ti’s poison with supernatural power. Any creature poisoned by the Yuan-Ti must succeed on a constitution saving throw (save = 8 + con + proficiency bonus) or be unable to turn invisible for 1 minute.  

Wildshape

Once per day, the yuan-ti can use its action to wildshape into a swarm of poisonous snakes, or into a giant constrictor snake, or back into its true form. Maximum duration in hours equals 1/4 of total character level (minimum of 1 hour).