A sketch of Lady Indusia, mantis lich, by  crovirus!

Indusia was a benevolent witch in life, one who lived in a rural village. She aided all her neighbors to the best of her ability, but drew scorn from the paranoid, superstitious mayor of her hamlet. When she began dabbling in black magic to eliminate a strange plague on the local crops, the mayor pounced, whipping up a mob that drug her to the town square, where he had her beheaded. Unfortunately for the mayor, the sheer amount of black magic Indusia had been absorbing saw fit to reanimate her headless form.

And that magic was hungry.

Indusia awoke to find the partly-devoured remains of the mayor and those who once were her friends staring on in horror. She ran to her home and wept, only emerging days later with a shadowy illusion where her head once was.

In order to keep "alive", her body occasionally falls completely under the control of her magic... and heads off to feed on living flesh. Once her unholy appetite is sated, she comes to her senses and mourns.