Mummies
Mummies tend not to come back to life on the Discworld. There are only two cultures (Djelibeybi and Tsort) who really believed in mummification anyway, and they have both lost interest in it in recent years. While the original purpose of the Discworld's pyramids was to bend time and create stasis in the central chamber, so that a dying ruler interred there would never completely die, the message got lost along the way, and eventually the mummification process became a case of removing the ruler's organs, drying them in salt, wrapping them in bandages etc. Pyramids, however, describes an occasion when the dead of Djelibeybi did return to their bodies. Essentially they seemed much like zombies, only better preserved. All of them retained what memories they had from the time in which they were alive. They unanimously despised the pyramids in which they were interred, and upon their release they helped to destroy the Great Pyramid and then dissolved their corporeal bodies in the Djel river. This caused some problems for Death, as he was unused to having over 1,300 souls to take at one time (he eventually processed them in queue). Prior to the events of Pyramids, the souls of those mummified appear to have been prevented from totally dying, and were instead trapped within their pyramids.
Read more about this topic: Undead (Discworld)