Melanie is a lamia, a shapeshifter capable of turning her legs into a multicolored serpent's tail. She has retractable fangs in her mouth and is venomous. Her hair is long and black.
Melanie can turn humans into snake people, and in the Circus of the Damned has done so for a group of willing men, her harem of potential mates. She is apparently a true immortal and does not appear to be killable by any means, although this does not hold true for the men she is transforming.
The first time we see Melanie she is a member of Mr. Oliver's retinue, but ultimately gets a job as a member of Jean-Claude's circus troupe, performing at the Circus of the Damned. She has mostly behaved herself ever since.