Hear me out, this has gotta be a primarily desert-based region. You’ve got some obvious gimees with: Cacturne, Drapion, Cofagrigus, Krookodile, Flygon, Darmanitan, Gliscor, Lycanroc, Arbok, Volcarona and Lucario lines. There’s also a lot of Rock, Ground, Steel and Fire types in general.
Another touch that works is that the Ice types mostly either would be extinct/diminished (Mamoswine and Aurorus) dating back to when the region may have been colder, or Pokemon like Abomasnow and Ninetales-Alola that can create their own cold environment. Something like Glalie or Eiscue could reasonably live in a cooler underground cave, or in that cooler environment from Abomasnow.
Most of the Water types wouldn’t actually need a huge body of water to survive since they can be at home on land (Golduck, Cramorant, Slowbro, Kingler, Golisopod, Quagsire, Gastrodon, the starters). The only water types that we haven’t seen live on land are Jellicent, Lanturn, Kingdra, and Relicanth who could be saved for a larger body of water.
There are only a small handful that would feel out of the ordinary for the desert theme besides those already mentioned, but I think a compelling home could be given to each.
Tsareena, Tangrowth and Ambipom (oasis)
Eelektross (Nile river stand-in if you’re doing an Egypt thing, cave otherwise)
Swanna (kept by a rich guy in the largest city)
Foongus and Breloom (imported for medicinal use, can be obtained in trades)
