The Mummy is a hostile mob added by the Project Zulu mod. It may spawn naturally in desert biomes. When fighting "stage 2" Pharaoh boss, he summons mummy armies. Mummies drop emerald shards and experience, but nothing of value.
Mummies can climb on all natural blocks, including cactus which can result in "suicide" due to not jumping off high ledges, so they could die on top of the cactus. Mummies can only spawn in deserts, and are fairly common.