Mummies are common enemies in the Temple and in the City of Gold that will wander in a horizontal line, spewing flies if the Spelunker gets within its range and dropping two rubies if killed. Their flies can hurt other Monsters and can also be whipped out of the way, although this can be a dangerous action if close to a Mummy as they can spew several swarms in a few seconds.
Always take extra care when approaching them, as getting hit by one exploding fly often means getting stun locked to death by the barrages that follow, regardless of how much health you have. However with spike shoes/some extra sticky bombs or ranged weapons, they are usually fairly easy to eliminate, so long as you don't let them surprise you. Furthermore luring them into tiki traps or lava will make short work of them.
If you don't have access to any of these, then its best to avoid them while you can, though you can jump on/bounce off the head without harm, even without the spike boots.
Much like other undead enemies, Mummies do not drop blood when hit or killed, though this doesn't make them any less useful if the Spelunker has the Kapala as their vomit droplets can be used to fill it (if you can get to a safe position, where the terrain blocks the flies).