The Meaning of Life, the Universe, and Everything.
Simply before you say this is redundant, I'm supporting the idea by CursedGhast and BaxterNikolai.
Anyways lets start with the mummy. The desert temple should have spawners throughout the desert temple that spawn mummies. The mummies should look like a thing wrapped in those straps and with red eyes peeking through two holes. It should be similar to the zombie. Same groan. Or it could be a textured zombie that looks like a mummy when its in a desert biome. You choose.
Next and last, the desert temple. You go in, drop down, get the loot, build back up, and leave, Pretty bland right? Well there should be more. Parkour, traps, mobs, and of course, LOOT! It should be more of an adventure then just the old tnt trap. Lets try to make this game a little more adventurous in the desert temples.
I wouldn't call this completely vague, but you didn't provide just enough detail. You should specify what the parkour and traps would be like, and how/what monsters will spawn there.
When making a suggestion, never say "You choose". It generally just ticks people off.
Well what I'm thinking for the parkour is maybe like you have to jump on poles and if you fall, there will be mobs ready to eat you, and you'll need blocks to get back up. One traps should be a tripwire and once u step over it a bunch of sand will fall on u and u should suffocate. I'm thinking of other things at the moment for like parkour and traps. What mobs might spawn in parkour/trap, most hostile ones. All of them except the creeper cuz u could be in the range and it might explode. Also, no skeletons. They'll just keep shooting you off. So probably spiders, mummies (if they were to be added), and zombies.