ToME Wiki
Wraithform: similar alternatives?
The wraithform that existed in ToME 2 is fun and useful, although I could see other "cosmetic" variations on that theme. Becoming a light-hating ghost isn't the only possible way to pass walls; other magic can allow the same power with different weaknesses:
Ethereal form: hurt by nether (or some equivalent damage which affects the spirit directly); can pass through any non-permanent barriers except trees (any other living thing blocks their way).
Cloud form: hurt by heat (which disperses it) and cold (which condenses it); can pass over non-permanent trees and mountains.
Stone form: hurt by acid (which eats rock quickly); can pass through any non-permanent rock without digging.
I can easily imagine nature magicians favoring the last two, while mind/spirit magicians preferred the first...leaving the "basic" wraithform for those who favored necromancy/shadow spells.