I have been on some good pain pills lately and they seem to be opening my mind to other ideas for mechanics.
I had an idea for preserver that only relies on tapping into your own lifeforce to power spells. I’m sure it has been done before somewhere, but I haven’t seen one solely devoted to self defling.
My idea is this, the cost in hit points to cast the spell doubles each spell level. The damage being necrotic, or whatever the equivalent is in your version of the game. So the cost would look like this…
1st level spell: 1 hp
2nd level spell: 2 hp
3rd level spell: 4 hp
4th level spell: 8 hp
5th level spell: 16 hp
6th level spell: 32 hp
7th level spell: 64 hp
8th level spell: 128 hp
9th level spell: 256 hp
10th level spell: 512 hp.
Of course the higher level spells would kill the caster outright unless that caster had resistance to the magic type, but I have the idea that the caster could split the damage done to self between the environment and their self. Of course if the caster could use hostiles HP to power the spell, they could be insta kills at high level, but spread across many enemies it might not be that powerful.
I’d have to figure out how all that worked, but thought I’d run it by you folks for suggestions to make it balanced.
Another idea at higher level is Grey casting, using the life forces in the Grey to power half the spell, so then the caster only takes half damage.