Schattenalfen & Psionics?
by Marc SaindonI'm not much of a fan of psionics, although with Subclasses like the Psi Warrior (Fighter), Soulknife (Rogue) amd Aberrant (Sorcerer) in 5e and 5.5e, wedging them into the Mystara without changing too much in the retcon is a bit complicated. I've thought that this could work with the more isolated Shadow Elves, but they already have a detailed sourcebook to draw upon.
Instead, I've figured maybe their less friendly cousins, the Hollow World's Schattenalfen, might play the role. Sure, they're written as "Morlocks" that prey on the Azcans as rivals in a bid to serve the same entropic Immortal Atzanteotl, but the boxset clearly indicates that this isn't all of the Schattenalfen, but how their society because of one dominant evil group (the same applies to the Azcans). One idea is that a side-effect from the Schattenalfen's vulnerability to sunlight (truly a bane in Hollow World, where the sun never sets) is that they do have a greater tendency to develop psionic powers (think of the human psychic mutants from Beneath the Planet of the Apes), which sets them apart from the friendlier Rafiel-worshipping Shadow Elves of the Gazetteers.
Psionics, an internal power, one not granted by Atzanteotl, an external source, of course upsets the status quo and the hierarchy of Schattenalfen society, so there are times when these people are marginalized, face persecution, or are outright outlawed and exiled (leaving these vulnerable to Azcan attacks). In order instances, especially when the Schattenalfen are facing setbacks from Azcan incursions, the society cycles back to being more tolerant in an effort to preserve itself from outside attacks. Thus the Psi Warriors, Soulknives and Aberrant Sorcerers would slowly find themselves a place as a counter-power against the Clerics of Atzanteotl, perhaps tapping into the original Chaos versus Order alignment rivalry of BECMI (which ignores Good and Evil tangents).
Some Psionics might be rugged individualists, others true revolutionaries, while quite a few might just be simple opportunists (who see chaos as a ladder).
Image from: https://www.deviantart.com/wellowr/art/The-Pale-Warrior-Elf-1109680185