I doubt this would be created, as I type this out I can envision a good number of code changes it would require. However - Astral form?
What I envision for Astral Form is the following gains:
Immune to physical damage (perhaps outside of party formation, like ethereal form)
Increase to magical power (spell level?)
Auto-bypass resistance (Woot MR barbs?)
Can not attack physically.
Concentration required increase for all spells.
Cons:
Leave their body/gear behind
Damage taken directly to mana (probably at a decreased percentage)
When spell drops, shaman returns to body, if it is in the room or carried by someone in the room. If it is not in the room, the shaman becomes a spirit.
More susceptable to dispelling magic.
Code:
[Spells Help] Astral form
Syntax: cast 'astral form'
By casting aside their physical form, a shaman can take on the form of their
ancestors. In this form they can not be struck upon by physical or arcane
blows but in turn are unable to attack their foes directly. While in this form
their spells can not be resisted but in turn they also have no innate magical
resistance either. Damage taken to the shaman shall directly affect his
magical energies. When the spell ends, the shaman either returns to its body
or to the river.