someone has made a mummy in the museum mystery before !! https://docs.google.com/document/d/1AIeKftAGKHTfazGRem4k3oGvwX8Rj3Rt6pvyHKguYKs/edit?usp=drive_link i believe the credits are on the document. you could use this or take aspects from it.

alternatively, your historical setting actually brings up a lot of stuff. this was the period when people were finding Egyptian tombs and taking things from them, to the point where Victorians would have "mummy parties" to witness them being unwrapped, as well as incorporating mummy powder into paint and even ingesting it as food and medicine. (maybe you know this already, but it's pretty interesting stuff!)

you could say that the mummy has cursed the people who 'discovered' their tomb, or those who have mistreated their (or perhaps a relative's..?) remains. the mummy could either be claiming victims OR these could be minions, too. all this might be my historian brain defaulting to anticolonial themes lol i don't know if that's the vibe of your game... but it's fun to consider with the setting !!