"Duchess Epidermis", "Erzsébet Báthory", "Bone Witch" (Her real name is unknown) is a Delta-Class Threat in Electrophoresis. Having holed herself up in the ruins of Hungary after developing her power, Duchess Epidermis has ruled the empty kingdom for a number of years, maintaning minimal contact with outside powers in that time.
She fancies herself a gardener, and while it is unknown to the readers what her power is at this time, conjecture points to a form of biokinesis, allowing her to inflict bodily horror on others freely. According to one poster on the forums:
"She is known to be incredibly unstable and prone to violent outbursts, and appears mildly incapable of listening to or comprehending concepts like 'we surrender please let us go' and 'we're retreating'. Also she apparently likes gardening, possibly a deadly euphemism for what she does to people. Or maybe it’s an actual garden. I don’t know which is scarier."
In the ChiasmARG, she was one of the first discussions on the Chiasm Forums, detailing her conflict with Typhon.
In other universes
In the PMMM fan universe, Duchess Epidermis is an evil, veteran Puella Magi who collects souls much like Souju does.
She appears on the Empress card in the Electrophoresis tarot.
The term 'Epidermis' refers to the outer layer of the skin. (dermis = skin)