[konidias]

Simple solution: Lower the damage that Flaming Aura deals, and edit Balor to balance things. For example:

Balor Demon King, Duke of Hell, Tempter and Tormentor

Repelled: Protection, Restoration
Denied: n/a
Special: Health_Regen -2, Spell_Regen -1, Luck -1, -5 Resist_Cold (which means maximum resistance to cold is 90% instead of 95%)

Granted Spell(s): Flaming Aura (medium level), Rage (medium level), Vitriol (medium level)
Altar Effect(s): Remove Curse, Enchant Weapon (medium)
Holy Relic(s): n/a

Just remove the underlined parts, and lower flaming aura. That way, aura still does some damage, though less than before, yet health regen and cold resistance are no longer affected.