To be honest, thanks to the use of psionic powers many monsters from both of these sources slot right into Dark Sun. There is, HOWEVER, a major sticking point I have with the site’s own monstrous bestiary. Yes, I’m going to pick a fight over this!
Psionic Bestiary (Dreamscarred Press)
It’s almost easier to list the ones that don’t fit.
Automatons and phrenic hegemony- These are extra planar invaders. Aside from the constant controversy over how planar isolated Athas is, why would anyone want to invade Athas? You’d be squeezing blood out of a very spikey nasty stone. I am sure you can find a reason, but there is plenty to Athas specific that’s well worth exploring, without importing something that out there!
Remnants of the Cleansing Wars- Many psionic beasts and constructs could easily come from this. Psion-killer golems come to mind. However, I want to highlight the Ural and the Unbodied in particular. The latter are psionic minds that have gone “Gamesters of Triskelion.” Disembodied psionic minds. What if they did that to escape Cleansing? And the Urals are another result of powerful psions attempting to survive a catastrophe, but in their case they have powerful physical bodies, but are reduced to gibbering idiots.
Verizal- I like these guys as a good replacement for mind flayers. Mind flayers feel too generic to me.
Once again, many work. Some highlights follow.
Cerebric Cyst- A buffed brain ooze.
Chyzaedu- I’ll admit, I have a hard time finding stacks for psurlons. I would use these guys instead.
Combusted- Psionic, undead and on fire? Sounds Athasian to me!
Echohusk- Psionic version of zombies
Egophage- Buffed up, evovled version of the intellect devourer.
Hive Mind Beetle Swarm- fascinating and weird combination of psionics and swarming insects. The possibilites are endless.
Those are just some of favorites that occur to me. To be honest, there is a lot of standard monsters in there but with psionic powers or a psionic variant. Whether you like that or find it useful is up to you.
So here is the fight I said I would pick. The Terrors of Athas on this (honestly awesome site) list “blue” under the allowable monsters. The Blue are a variant version of goblins. The goblins are extinct. How can this BE? HOW? HOOOOW?
Thanks for your time