There are 3 in one tomb in China, you will have to fight them all, but, don't worry, you won't be able to get near them until you have completed the tournement. Mummies are no match for a martial arts black belt. There is also another tomb where a mummy may appear, but the chance is very small. I would suggest, if you don't have martial arts maxed you carry a mummy snack with you when going into the second tomb under the market (Dong Ho's Treasure - or something like that, it's a long time since I did that one.)
There are several tombs in Egypt which have predictable mummies, and, at least 3 more with randomly occuring mummies. Same advice as above if you don't have martial arts. One mummy appears fairly regularly in the third of the row of pyramids, the one you can enter without a challenge.
Mummy's always appear from sarcophagus'. Most, but not all, require you to open the sarcophagus, so these can also be avoided if you do not want to risk the curse and do not have snacks or martial arts skills. Incidently, the easiest way I know of to cure the curse is the moodlet manager.
