Not a custom I was planning, but I bought a bundle of BtVS Deluxe figures dirt cheap and realised that the base body works pretty well for Callisto's non-costume.

The head is from ML Xorn (Magneto) - she is/was supposed to be ugly... :O) Sculpted the hair and eye patch with green stuff, added some sinewy looking muscles to her arms (female toy arms too often have zero definition and she is supposed to be a tough brawler), used various straps for the studded collar, arm bands (these also hide the wrist swivels) and belts, chopped up the Faith jacket to turn it into a ripped waist vest thing, shortened the legs, filled the peg holes as always and added the knife from my bits box. The trousers have a varnish coat over them for that tight leather look.

Fairly quick and simple.