I love Yaun-ti, I'd love to see some Yaun-ti shenanigans thrown into the mix by some of our DM's some day.
You could play a snake cultist, or a native from Toril, that gives you lots of options. As an out lander from Chult, or Calimshan you could have a fascination for snakes, venom, and lurking in the shadows. One of my favorite Goddesses is Talona, the Lady of Poison, Mistress of Disease, and Mother of All Plagues, she would make an excellent deity for a character who likes to use poison and diseases, who venerates snakes, frogs, reptiles, and other poisonous/venomous creatures. Or you could play as a Mulhorandi from Thay. If you wanted to be a Ravenloft native you can choose Set as a deity, and be a native from Har'Akir. You have lots of options, you might even get swome other players who want to rock up similar characters and create a cult of your own.