Based on discussion in this thread A New Mythic Approaches – Cailleach - #8 by Risa , I propose this change to Mana Burn effect:
Mana burn: Deal damage equal to target’s current mana plus caster’s magic (this part remains the same as current), then apply Mana Boiled status on target.
Mana Boiled: Negative status (debuff). At the start of turn, drain 2 mana, then deal damage to self equal to new current mana. If current mana reaches 0 at this moment, this status is removed. This debuff can also wear off like most other debuffs. Mana Boiled and Enchanted cancels each other (just like Blessed and Cursed cancels each other). This cancelling effect happens before checking for immunity, so that applying mana boiled effect onto enchanted troop that immune to mana boiled will still remove enchanted buff.
Change immunity to mana burn in traits Impervious, Mana Shield, Sky Ancestry and status Blessed to immunity of mana boiled. Also, add immunity to mana boiled to Dark Ancestry, High Ancestry, and Wood Ancestry. (Because these sub-races of elf have immunity to mana drain, which would make them sustain more damage due to mana boiled.)
This rework makes sure spell damage from mana burn spells will not be blocked by immunities (very common these days), while keep its distinct flavor mostly intact.