>>10907132You don't. At least, not anymore.
Mummies come from Irem, the City of Pillars, seat of the Nameless Empire. A predynastic Egyptian empire with a fairly oppressive caste system of Guilds that has since been lost to time. Irem was lead by the Shan'iatu, sorcerer-priests of incredible power, and after about a century of conquest they decided that they deserved true immortality and set about experimenting. Countless souls were sacrificed to refine necromantic rituals, each failure brought their victims unspeakable horror, but was a step closer to their goal. Eventually they succeeded and perfected what would be called the Rite of Return. The Rite of Return is how you make a Mummy but Irem is gone and with it so too is the knowledge of the Rite of Return.
As you might imagine the first step is ritual mummification. Candidates were chosen by the Shan'iatu from the major Guilds of Irem. Every internal organ except for the heart is removed, the brain is scraped out of its skull. The empty body cavities were then filled with perfumed herbs, which means all mummies smell sickly sweet and floral. This whole process does mean that they die, for a time. During this death their souls are sent to the depths of Duat, the Underworld
(but a different underworld to Geist's), in which their souls are torn apart, examined, assessed, and reassembled in what eventually becomes a mummy. This process is performed but the 42 Judges of Duat, godlike beings that assess the worthiness of souls and that each Arisen must make a pledge to. Before a Mummy makes this Decree the Judges test their Ab (heart), Ba (spirit), Ka (essence), Ren (name), and Sheut (shadow), the aspects of their five-fold soul in order to determine who the Mummy really is on their deepest level and the Decree in which they belong. These tests aren't always the same but they are always harrowing. Testing their Ab might involve forcing them to chose between murdering their sister or their brother, or it might be reuniting with a past lover, or facing a bitter rival in contest.
With each trial they pass they feel stronger, every torment sharpens their mind, as with each step they take Sehkem course through them. Pure lifeforce granted by the Judges and after their final trial their soul burns bright with it and they have a true understanding of themselves. This is when they make their Decree, each Judge has it's own purview and the Mummy will invariable pledge their service to the Judge who's purpose most resonates with them. Afterwards they open their eyes in a new time and place, unsure of who they are as their memory slips from them. Overtime they will regain it and with-it understand part of their place in the world. But the Sekhem that grants them such incredible powers is fleeting, as they stay awake it ebbs from them, slowly they weaken and eventually will crumble. When that happens, or they perish through violence or accident, the awaken in Duat to be tested again. Their Judge will assess them, perhaps reward them, perhaps punish them, but mummies rarely get to escape the cycle. Eventually they'll be called to action again whether that's their Judge's doing, their Cult's, a disturbance in their tomb, or greater cosmological phenomenon. They'll open their eyes in a new time, forwards or backwards, and remember little of who they are. Mummies aren't just immortal they're timeless, the Rite of Return kinda broke the world and so time is very strange for the Arisen. They awake non-linearly, can exist in alternate timelines, can sense the flows of time, and are generally walking paradoxes. Time is broken, Mummies don't seem to mind.
It also means that Mages can't use Fate or Time magic on them 