The planar cosmology of Athas differs from the rest of the D&D multiverse. Even the Inner Planes are different. How do the Positive and Negative Energy Planes interact with Athas, and what would their clerics look like?
I used the concept that the positive energy of Athas flows from the elemental planes on outwards. Quasi-elementals and that energy manipulation would be pretty tied together in that regard. The way I was introducing the “negative” was more as an incursion/decaying of the elemental planes after the millennia of war on Athas’s surface.