Hmmm.... just throwing craziness out off the top of my head:
Stoneform (80 piety)
Immune to Mana Burn, Poison
Passive regeneration permanently disabled
IMAWAL costs 0 mana to cast
Every time you petrify a monster (bloodless enemies - ie plants - do not count) you gain 20% of your max mana and max HP back, and gain a permanent +1 bonus to base attack.