Yuan Ti have been my favorite D&D monsters ever since Monster Manual 2 was published. Here's my version for S&W WhiteBox.
Yuan Ti, Abomination
Armor Class: 0 
Hit Dice: 9
Attacks: sword (1d6)
Yuan Ti abominations have a snake body and snake head, with the scaled human torso and arms. They can use weapons, and cast spells. They can see in the dark, including magical darkness. They can cast the following spells once per day: Cause Fear, Dark I, Sticks to Snakes, Neutralize Poison, Suggestion, and Polymorph.
Cause Fear: Target must make a Saving Throw or run away from the caster for 1d6 rounds.
Suggestion: Target must make a Saving Throw or follow a one sentence command from the caster. Target will not attack his friends or himself.
There is also a pdf version (with borrowed 1e illustration) HERE.