Kaptain_Kantrip
First Post
I am currently in a campaign featuring extensive use of yuan-ti and one of the players wants to become one because he has fallen madly in love with one of their halfblood priestesses, LOL. This won't disrupt the campaign since it's an evil one. 
So looking through the Tome & Blood splatbook, I was inspired by the Dragon Disciple PrC. My PrC here ends up by 5th level granting all psionic and spell-like abilities of the yuan-ti, SR 16, Natural Armor +1, and +3 levels of existing spellcasting class (presumably cleric). The character's type changes to Monstrous Humanoid and they are basically considered a yuan-ti pureblood for all purposes. They don't gain the feats or ability scores of a yuan-ti, however; they retain their own in all cases.
Yuan-Ti Disciple Prestige Class
The Yuan-Ti Disciple (YTD) is a human who has willingly taken on the corrupted
bloodline of the yuan-ti. Initially, the power of the bloodline unlocks certain latent psionic
talents lying dormant in the disciple’s mind, as well as generating a rudimentary spell
resistance and natural armor bonus. As the disciple progresses down this path, more psionic
powers are unlocked, until the disciple has achieved mastery of all psionic powers
common to yuan-ti. In the final stage, the disciple becomes a yuan-ti pureblood, gaining
the spell-like abilities of that creature (see Monster Manual, p.190).
Requirements:
Race: Human.
Alignment: Any evil.
Feats: Dodge, Improved Initiative
Skills: Knowledge (Religion) 8 ranks.
Languages: Yuan-Ti.
Spells: Ability to cast divine spells and access at least one of the Chaos, Evil, Destruction,
Plant domains (or another domain granted by a yuan-ti deity).
Special: Must be willingly transformed through a ritual performed by a yuan-ti cleric
wherein the character to be transformed renounces their humanity and consumes a
mouthful of the sacred blood of the initiating cleric, as well as sacrifices a human life in the name of the yuan-ti deity.
Hit Die: d8.
Class Skills: Bluff, Concentration, Craft, Diplomacy, Hide, Intimidate, Knowledge
(Religion), Listen, Move Silently, Spot.
Skill Points at Each Level: 2 + Int modifier.
Ex-Yuan-Ti Disciples: Only a wish or miracle can reverse the transformation process;
the character cannot willingly become of a non-evil alignment or seek to regain their
humanity. If somehow they ever regain their humanity, they lose all class abilities and
cannot advance levels in the Yuan-Ti Disciple class.
Table 1-1: The Yuan-Ti Disciple
1st Level: BAB +0, Fort +0, Ref +2, Will +2
Special: +1 natural armor, SR 11 + 1 per class level.
2nd Level: BAB +1, Fort +0, Ref +3, Will +3
Special: Produce Acid (1d6 damage by touch only, at will), Detect Poison (at will); both
of these are psionic abilities. +1 level of existing spellcasting class.
3rd Level: BAB +2, Fort +1, Ref +3, Will +3
Special: Chameleon Power (+8 Hide checks, at will), Alternate Form (tiny to large viper,
at will); both of these are psionic abilities. +1 level of existing spellcasting class.
4th Level: BAB +3, Fort +1, Ref +4, Will +4
Special: Aversion (inspires fear of snakes and yuan-ti, including the character, at will);
this is a psionic ability. +1 level of existing spellcasting class.
5th Level: BAB +3, Fort +1, Ref +4, Will +4
Special: Yuan-ti Apotheosis (character gains the spell-like abilities of a pureblood yuan-ti
and changes to the monstrous humanoid type).
* Unless otherwise noted, all psionic and spell-like abilities are exactly as per the yuan-ti
entry in the Monster Manual, p.190.

So looking through the Tome & Blood splatbook, I was inspired by the Dragon Disciple PrC. My PrC here ends up by 5th level granting all psionic and spell-like abilities of the yuan-ti, SR 16, Natural Armor +1, and +3 levels of existing spellcasting class (presumably cleric). The character's type changes to Monstrous Humanoid and they are basically considered a yuan-ti pureblood for all purposes. They don't gain the feats or ability scores of a yuan-ti, however; they retain their own in all cases.
Yuan-Ti Disciple Prestige Class
The Yuan-Ti Disciple (YTD) is a human who has willingly taken on the corrupted
bloodline of the yuan-ti. Initially, the power of the bloodline unlocks certain latent psionic
talents lying dormant in the disciple’s mind, as well as generating a rudimentary spell
resistance and natural armor bonus. As the disciple progresses down this path, more psionic
powers are unlocked, until the disciple has achieved mastery of all psionic powers
common to yuan-ti. In the final stage, the disciple becomes a yuan-ti pureblood, gaining
the spell-like abilities of that creature (see Monster Manual, p.190).
Requirements:
Race: Human.
Alignment: Any evil.
Feats: Dodge, Improved Initiative
Skills: Knowledge (Religion) 8 ranks.
Languages: Yuan-Ti.
Spells: Ability to cast divine spells and access at least one of the Chaos, Evil, Destruction,
Plant domains (or another domain granted by a yuan-ti deity).
Special: Must be willingly transformed through a ritual performed by a yuan-ti cleric
wherein the character to be transformed renounces their humanity and consumes a
mouthful of the sacred blood of the initiating cleric, as well as sacrifices a human life in the name of the yuan-ti deity.
Hit Die: d8.
Class Skills: Bluff, Concentration, Craft, Diplomacy, Hide, Intimidate, Knowledge
(Religion), Listen, Move Silently, Spot.
Skill Points at Each Level: 2 + Int modifier.
Ex-Yuan-Ti Disciples: Only a wish or miracle can reverse the transformation process;
the character cannot willingly become of a non-evil alignment or seek to regain their
humanity. If somehow they ever regain their humanity, they lose all class abilities and
cannot advance levels in the Yuan-Ti Disciple class.
Table 1-1: The Yuan-Ti Disciple
1st Level: BAB +0, Fort +0, Ref +2, Will +2
Special: +1 natural armor, SR 11 + 1 per class level.
2nd Level: BAB +1, Fort +0, Ref +3, Will +3
Special: Produce Acid (1d6 damage by touch only, at will), Detect Poison (at will); both
of these are psionic abilities. +1 level of existing spellcasting class.
3rd Level: BAB +2, Fort +1, Ref +3, Will +3
Special: Chameleon Power (+8 Hide checks, at will), Alternate Form (tiny to large viper,
at will); both of these are psionic abilities. +1 level of existing spellcasting class.
4th Level: BAB +3, Fort +1, Ref +4, Will +4
Special: Aversion (inspires fear of snakes and yuan-ti, including the character, at will);
this is a psionic ability. +1 level of existing spellcasting class.
5th Level: BAB +3, Fort +1, Ref +4, Will +4
Special: Yuan-ti Apotheosis (character gains the spell-like abilities of a pureblood yuan-ti
and changes to the monstrous humanoid type).
* Unless otherwise noted, all psionic and spell-like abilities are exactly as per the yuan-ti
entry in the Monster Manual, p.190.