I haven't read through all of these, so maybe this has been mentioned, but I would like a dark spell that allows you to either sacrifice life or gain damage to increase your mana. It could be precise
This mage immediately gains 2 tainted markers and 6 mana
or
Roll 8 attack die- the mage loses rolled amount of life, and adds the rolled amount to his/her mana pool.
It would probably need to be epic. Main thing would be the proper balance between life and mana. should it be 1:1? More life lost than mana gained? The other way around?