Mummy

The mummy is a new Life State introduced in The Sims 3 World Adventures. Normally, mummies are NPCs but sleeping in a cursed sarcophagus can turn a Sim into one.

Al Simhara
In Al Simhara, their home nation, NPC mummy will normally be inside their sarcophagus resting. However, upon detecting a Sim disturbing their eternal sleep, they will rise from their sarcophagus (you can sleep in a "cursed sarcophagus of the kings" but you have to do it several times to become a mummy, the blessed sarcophagus of the kings can turn you back the same way.) and pick a fight with the Sim that is treasure hunting. If the Sim happens to have a Mummy Snack in their inventory, the mummy will automatically remove it and return to their sarcophagus until they are disturbed again. If the Sim loses the match, they may become cursed. The Sim must plead with the sphinx, explore it completely, and use "cleanse" interaction on a special statue or the Sim will pass away within 2 weeks.

Biology
Mummies are covered in old, flammable rags. Thus if they catch fire, instead of the usual hour a Sim has before he turns into ashes, a mummy will die instantly. Also, mummies are very slow, so a Sim can outrun a mummy if he can flee the ruin he is in. However, being a mummy has it's perks as they are very strong in comparison to normal Sims, so Sims are normally outmatched by mummies unless they have a high Martial Arts skill level. A mummy can outlive a normal Sim by quite a few days. Also, their energy and bladder needs never decay.

Becoming a Mummy
Sims are able to become a mummy themselves by sleeping in a Cursed Sarcophagus of the Kings twice for a few hours. The first time they emerge, a message will appear saying that your Sim is slightly closer to the mummy world somehow. The next time you sleep, you will emerge as a full-blown mummy.

Reverse
To reverse the life state and become a normal Sim again, simply sleep in the Blessed Sarcophagus of the Kings for a day or so, when you emerge you will no longer be a mummy.