pause and have 3 mages all cast spell immunity, in my party one sorc had g acutiy on, so it might be best to have a sorc cast greater acuity...i dont have a non hacked bun bun led superparty, so just see if it works...anyway, have 3 mages pause and cast spell immunity, unpause, and choose a immunity, after the first row of spell immunity buttons go away, the second set stays around, and around, and around....
it seems to be random between aerie and sola, but i made aerie immune to every school, then clicked on sola icon,and got out of the spell immunity buttons row....
but i was able to make aerie super stacked spell immune, just like a sorc....using one stinky spell....its just a game bug, but for a few turns, i think its a few turns, you can make one npc totally immune to every school...