Okay, I don't actually have enough energy to go full autist here - in truth, I am kind of crashing - but we can irreverently gallop through the basics.
So. Mummies.
Long, long time ago, Osiris, the good guy of oWoD went "Shit, we need more good guys here" and cast a necromancy spell that produced a bunch of reincarnating immortal mages that are all supposed to be pretty chill. Then after a long nap, he woke up, saw that a lot of things happened while he was asleep and tweaked it to function a little better. Boom, pre-history is done. Osiris was a swell dude.
Basically, they are a spellcaster splat with access to a bunch of special bandage babe magic powers; Nomenclature (true name magic, basically Do Everything magic), Alchemy (potions), Amulets, (wards, self-buffs, miscellania), Celestial (divination, weather, fate ninja nonsense, retcons and time manipulation) Effigy (craft Pokemon, summons, yugioh), Necromancy (Good Vibes, healing, soul, therapy, talking with your grandmother, visiting your boss).
At high enough dots, powers kinda blend into each other. Particularly amulets and Alchemy kinda evolve into "Do anything" paths. Nomenclature *starts* as a "do anything" part.
They got a mana-pool, of sorts, with their Mana being Sekhem; IIRC, their pools are not very impressive by numbers, but there are numerous Mage-like way to cheese that.
Published Mummy powers go from 1 to 8 dots. Sort of like DnD circles. Everything from 6 and onward are "Elder" powers; very special magic nonsense.
8 dot nomenclature power, for example, is this;
>Renaming the Hekau - The Amenti can rearrange the laws of a specific supernatural power, for example redefining the Discipline of a vampire or the paradigm of a mage.
Which ELI5 translates as "Your magic system works the way I said it works." It is a contested effect and stuff, but that's what a swole enough mummy can get up to.
Overall, they are a funny splat that could be seen as as inferior side-grade to Mage; they have inborn methods of self-resurrection, are more durable, don't need to deal with "overheat" mechanics like Paradox, but still got to pay for individual powers.
They also get some special stuff for having really, really high attributes - sort of like, if they are strong enough stuff starts getting magical, if they are beautiful enough its fae charm, etc.
All powers and basic actions in the system they are working in are typically success-dependent, meaning you roll your basic stats + you relevant skill, typically with a dice pools that can realistically produce 2-3 sux without cheese or godlike stats. If you roll really well, you do something extra or accomplish your goals with greater panache.
They are honestly a pretty cool splat and had potential to be pretty impactful, but Mummy was never really popular so. They just kinda never became relevant to anything in the broader metaplot, as disparate and incoherent it already is.
They don't have to be pseudo-egyptian waifus. Sometimes they are chinese waifus. Sometimes husbandos.
They hate evil stuff, and like nice things. Sadly, they exist in a setting that is called World of Darkness.
Aaaand I run out of gas.