Yuan-ti Tainted ones and their Viper Forms??

[Ashrem Bayle]

I'm about to build a 7th level Yuan-ti Psion (Savant).

Now, according to both Races of Faerun and Savage Species, they have the psionic ability to polymorph.

RoF says they can polymorph into "viper forms".

Savage Species says they can polymorph into "snake or snakelike forms only".

Now my question is:

What the crap do they mean? Any kind of snake? How about Naga? It seems their wording was a bit too vague.

Also, Savage species lists them as a +1 ECL race, while RoF has them as a +2 ECL. Anybody know which is right? I'm guessing RoF.

 

[Derulbaskul]

In the other yuan-ti descriptions it specifically mentions the size of the viper. I have then just used the stats from Animal appendix to MM1.

Isn't the tainted one shown the same way? If it isn't, I would allow it to assume the form of a viper sized from tiny to small.

Cheers
NPP