So, to move away from the classic mummy, we have this:
MummiesMummies are the remains of those who are obsessed with material wealth, spending their whole lives stepping on others in order to gather as much as they can. In death, their will is strong enough that their spirits remain in their body, focused protecting their wealth.
Over time the mummy's body dries out, taught, leathery skin stretching over tough, rubbery muscles, and the last remains of their humanity shrivels. A mummy whose wealth is threatened is a determined and deadly opponent who follow thieves across huge distances without needing to stop for food or rest.
As far as mechanics go, I would give them varying HD and AC dependent on their age and power, and some sort clairvoyance type thing to allow them to track their stolen goods. Some minor magic powers of the "wasting curse" type would be appropriate too.
They would be used as one off monsters in very specific locations for the most part and I wouldn't be afraid of throwing a high level one against a low level party, as a slow moving but hard to stop enemy. Just as the party think they are safe in the tavern and are dividing up the loot, smash!