As I played Minecraft for the past 5 years, I noticed that not a lot of people care about the desert biome. For me, I think that the desert just needs more mobs to gain popularity, and maybe they can drop loot such as crafting materials. My first mob suggestion is the Millipede. Those little fat worms with a lot of tiny legs, yeah those ones. They just look interesting to fit in th desert! What ideas I can give you for the Millipede, is their behavior. They are only hostile to you when you attack them. In real life, some Millipedes can be poisonous, so maybe you guys should make Millipedes give you a short amount of time of poison. And I don’t know if they do this but you should make them burrow into the sand and maybe when you dig down, you can find a Millipede nest! My imagination is just crazy.. The rest is up to you for the Millipede.