I have a player who has chosen to be a Yuan-ti Pureblood and she has latched onto the following two paragraphs from VGtM:

"The goal of every yuan-ti is to transform itself into the ideal combination of snake and humanoid. This attitude is reflected in yuan-ti society by a caste system, with status predicated on where a particular form of yuan-ti lies along the ladder of transformation."

"The yuan-ti know rituals that can transform an individual into a more powerful type. The cost and time required to perform the ritual is prohibitive, and as a result most yuan-ti never get the opportunity to undergo such a transformation. Every use of the ritual must be modified to suit the individual undergoing transformation, and requires rare herbs, exotic magical substances, snakes, and one or more humans to be sacrificed and eaten as part of the procedure."

Does anyone have any good suggestions for how to make this work?  Since a type of Malison is the next higher level in the hierarchy, I assume she would become one of the three types (most likely the Nightmare Speaker).  What should I do for stats?  What "rare herbs" and "exotic magical substances" would you suggest I require for the transformation to succeed?  In the event the transformation fails (for whatever reason), should she then become a lowly Broodguard instead of a Pureblood.  

Any ideas and/or suggestions would be greatly appreciated.  Thanks!

I am wanting to do this for my own character. I'll try to reply here when we come up with the component cost.

This was originally posted two years ago.  Regardless of the outcome, the OP is very, very unlikely to be still waiting on an answer.

But it should involve treacherous activities like exploring forbidden jungles, making deals with beings from other planes, and shopping at Whole Foods.

As 6thLyranGuard said, this is old, but there are rules for this in ToA.

Quote from jeepinbird >>

I have a player who has chosen to be a Yuan-ti Pureblood and she has latched onto the following two paragraphs from VGtM:

"The goal of every yuan-ti is to transform itself into the ideal combination of snake and humanoid. This attitude is reflected in yuan-ti society by a caste system, with status predicated on where a particular form of yuan-ti lies along the ladder of transformation."

"The yuan-ti know rituals that can transform an individual into a more powerful type. The cost and time required to perform the ritual is prohibitive, and as a result most yuan-ti never get the opportunity to undergo such a transformation. Every use of the ritual must be modified to suit the individual undergoing transformation, and requires rare herbs, exotic magical substances, snakes, and one or more humans to be sacrificed and eaten as part of the procedure."

Does anyone have any good suggestions for how to make this work?  Since a type of Malison is the next higher level in the hierarchy, I assume she would become one of the three types (most likely the Nightmare Speaker).  What should I do for stats?  What "rare herbs" and "exotic magical substances" would you suggest I require for the transformation to succeed?  In the event the transformation fails (for whatever reason), should she then become a lowly Broodguard instead of a Pureblood.  

Any ideas and/or suggestions would be greatly appreciated.  Thanks!

1. First of all, the Nightmare Speaker is at least two steps above a Pureblood, since a Nightmare Speaker starts as a Malison and then uses a ritual to upgrade themselves (by pacting with Dendar).  If you want to allow this, the next step up is Malison.  Here's an approximation of the Malison rules:
   1. Lose the Poison Spray cantrip from the Yuan-Ti's racial powers.  Gain the ability to polymorph, self only, into a Medium snake, like a Malison can.
   2. Roll 1d3 to determine Malison type.
      1. Snake Head: You gain a racial bite.  It deals 1d4 piercing + 2d6 poison damage. 
      2. Snake Arms: You gain two racial bite weapons, as above; they have the light keyword.  You no longer have fingers.  Ask the GM's permission before doing anything that might require them, such as a Sleight of Hand check or a Thieves Tools check or calligraphy.
      3. Snake Tail: You gain a racial constrict weapon.  It deals 2d6 bludgeoning damage and a hit target is also grappled; until the grapple condition from this ends, the target is also restrained, and the constrict weapon cannot be used against any other targets.  You no longer have legs (or feet).  Without special GM permission, armor that fits you does not exist.  Ask the GM's permission before doing anything that might require legs, like riding a horse or climbing a ship's rigging.
2. Restrict knowledge of exactly how this ritual works; Purebloods are the absolute dregs of Yuan-ti society, and said society will want to keep tight control over which of them can rise up from the societal muck.  Only the very top echelons of Yuan-ti society should have a working knowledge of this - e.g. I would assume all anathemas know.
3. Rare herbs: Require a DC 20 Nature check, a DC 20 Herbalism Kit (Intelligence) check, and a DC 20 Religion check to tailor a menu of herbs and spices to this individual.  Lock at least one herb behind plot to acquire, such as a mushroom grown on diet consisting solely of the corpses of those who have never committed an evil act.
4. Exotic magical substances: Require a DC 20 Arcana check, a DC 20 Alchemy Kit (Intelligence) check, and a DC 20 Religion check to tailor a menu of magical substances to this individual.  Lock at least one substance behind plot to acquire, such as the yolk of a phoenix egg willingly given by its parent for this purpose, which must be swallowed by the ritual target during the ritual.
5. Broodguard is a fine punishment, but feel free to come up with other options as well, as long as you're forcing the PC to roll a new character.  For example, you could turn them into a snake familiar for a yuan-ti spellcaster. 

A malison is one level above, and a nightmare speaker is simply a specific type of malison rather than an additional level or rank. My character in particular is already a GoO pact warlock with Dendar as her patron and will be recieving the "recipe" for the ritual tailored specifically for her. However the ingredients, so to speak, will be prohibitive still. 

I see someone mentioned there were rules in ToA but I haven't found anything actually specific or helpful as far as laid out rules for this process. Are the rules brought by quindraco from ToA or made up? They seem made up. No offense though of course.

If this was my campaign, when the goal of the PC is reached the PC's story is done and the character becomes an NPC. The player would be free to join with a new character at that point.

Oof. Our characters all have multiple goals, both personal and campaign related. Also, I doubt fate will be so kind as to let them rest. So washing our hands of them after achieving something so trivial as evolving into a new creature form is out of the question. Essentially we are doing round robin DM style and plan to try and keep this particular party running indefinitely. Although I'm sure some deaths may occur. Anyway I guess it will be what it will. Thank you all for responding to my necromancy on this post lol. 

My point was that evolving into a new creature is anything but trivial. I'm all for homebrew but if a PC literally wants to become a monster, the easiest way to represent that is to make it a monster. Monster design is far removed from PC design with a lot less restrictions and trying to mash them together generally ends poorly.

The other way to handle it is to just RP the transformation and stick to the race rules they already have. Ultimately it's not really fair if one PC's RP goal is to put the ghost of their father to rest and the other's is to gain a bunch of stat boosts and free powers. I mean what's to stop the wizard from saying he wants to be a dragon, and now the druid wants to be an ancient treant and suddenly if your story doesn't account for wanting all this extra stuff, you fall behind.

I also want to make my character youn-ti I assume some priest could make you a stronger type but since youn-ti are literally snakes it would not be for free and you would probably have too do a side quest for them you might need too be high level and a lot of rare poisons and slaves would be required 

Am planning on playing as a Yuan-ti pureblood that wants to become a Yuan-ti anathema to build his own kingdom to push his race into a new age by leaving the old ways behind by using a wish spell or by other means but playing as a anathema would be game breaking so am going to have ability that lets me shift back into a pureblood that way am not going to wreck the campaign and lore wise traveling as a anathema is not a good idea you would get too much unwanted attention