Original Yuan-tis were created from human, yours doesn't have to be.
This sorcerous origin will take you through the evolution and the perks of turning into a Yuan-ti.
In my setting it was an botched ritual to awaken Merrshaulk that failed and turned the half-elf sacrifice into one of the most powerful servant of Merrshaulk and a vilain was born :)
Available in French & English. Let me know... [click here for more]