Ment
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I think the mana system could be simplified. You have three parameters: starting mana, mana regeneration rate, and spell cost. However, for most mages (except Ilanna), the ratio of mana regeneration to the total amount is roughly the same, not significantly different. I suggest fixing these parameters for all mages and balancing the spell costs instead.
For Ilanna, with only one spell, the numbers are such that she can essentially ignore mana altogether; you could simply set the spell's cooldown to "once every two nights." This seems like it would be equivalent, if I haven't missed anything.