Mummy

Some of the relics from our past aren't quite so...inert as you might hope.
- Rademes Abydos, Archivist of the First Tower, on mummies.
Theligosian customs surrounding the treatment of the dead are quite consistent across the entire culture. The body of the deceased is to be cremated, and their name memorialised in some way - whether that is in a fashion such as Liste's gardens, or the Velvet Way's wall of the dead.
Mummies, however, have not had their remains treated with such respect. They are relics from the Time of Strife - lawbreakers or rebellious men and women who defied their Infernal masters commands, or somehow offended them greatly.
Mummification was one of the harshest punishments meted out by the Hells. The guilty party would first have their organs removed and placed inside canopic jars, enchanted to preserve them in a "fresh" state such that the heart would still beat. They would then be wrapped in bandages from head to foot, and a curse placed upon them so that their soul could not leave their rapidly decaying body. Finally, they would be put to work as guards, standing an eternal vigil over their master's most prized possessions - still aware but unable to disobey, slowly being driven mad by the pain of their rotting flesh.

A Mummy can be released from their eternal torment only by the destruction of their canopic jars. Whilst their bodies can be burned, bludgeoned, or otherwise vaporised, as long as their jars remain they will slowly rebuild themselves.
Thankfully, no new Mummies have been made since The Rise of Man. Whilst the knowledge to do so almost certainly exists within the Deep Archives in She'Ammut, the process is considered far too abhorrent to inflict on anyone, even the vilest of criminals.