Pyreens are a non-playable demihuman race from the Dungeons & Dragons setting of Dark Sun. Born during the Rebirth at the start of the Green Age of Athas, they were created by the rhulisiti to be the defenders and protectors of Athas. As such, they are similar to 3.5 mongrelman in that they resemble a harmonious blending of the four main demihuman races - with the bodies of dwarfs, the ears of elves, the eyes of humans, and the faces of halflings - whilst at the same time possessing seemingly infinite lifespans, supra-genius (19+) Intelligence, and the powers of high-leveled multiclassing psion-druids.
You might be wondering how Athas ended up such a shithole with these guys around. Well, it's actually ironic: one Pyreen went screaming off the deep end and became convinced that the rhulisiti had made a huge mistake adapting themselves into different races, so he created defiling magic and organized a centuries-long, planet-ravaging genocidal campaign called the Cleansing Wars that wrecked the world as part of a mad plan to recreate the Blue Age. That fuckwit's name was Rajaat, and it's all his fault.
So, the surviving pyreens dedicate themselves to undoing what can be done. Which isn't easy, because there's only so many of them, there's a very big, ruined world to fix, and although they can cast the Rejuvenate spell, which reverses the damage done by defiling, they can only do so once per month.