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Magic Corruption Rules
For my Vornheim/Gaxen Kane game. Draft 1. Subject to change.
Each time an M-U spell is cast, caster must roll:
SL = "Spell Level"
CL = "Caster Level"
(SL ^ 2) / (10 * ( CL + 1 ) )
Round that fraction to the nearest 5%, and caster must beat it on a D20. 1 is always a failure, 20 is always a success.
If the roll fails, the caster must make a saving throw vs. magic with a penalty of the spell level (so, -1 for a first level spell, -3 for a third level spell, etc.)
If *that* saving throw fails, roll 1d6. The demon powering the spell:
1-3) devours 1dSL from a random ability score
4-5) devours 1dSL maximum hit points
6) confers a mutation: roll on the d100 mutation chart from http://monstermanualsewnfrompants.blogspot.com/2011/12/1d100-table-of-mutations-and-wait.html
We can also use this for "overcasting" ; each time you cast a previously-memorized spell no longer in memory, it is treated as if you added the spell level to the effective spell level.
Thus: you're a first level magic user with _Magic Missile_ memorized. You cast it. That creates a 1/20 chance of something bad happening.
Then, you cast it again: it's now an effective level of 2, so there's a 4/20 chance of mishap. Your third try? 9/20....and your saving throw penalty increases too.
And...you can do this for learning and casting spells too hard for you at your current level, as well.
Each time an M-U spell is cast, caster must roll:
SL = "Spell Level"
CL = "Caster Level"
(SL ^ 2) / (10 * ( CL + 1 ) )
Round that fraction to the nearest 5%, and caster must beat it on a D20. 1 is always a failure, 20 is always a success.
If the roll fails, the caster must make a saving throw vs. magic with a penalty of the spell level (so, -1 for a first level spell, -3 for a third level spell, etc.)
If *that* saving throw fails, roll 1d6. The demon powering the spell:
1-3) devours 1dSL from a random ability score
4-5) devours 1dSL maximum hit points
6) confers a mutation: roll on the d100 mutation chart from http://monstermanualsewnfrompants.blogspot.com/2011/12/1d100-table-of-mutations-and-wait.html
We can also use this for "overcasting" ; each time you cast a previously-memorized spell no longer in memory, it is treated as if you added the spell level to the effective spell level.
Thus: you're a first level magic user with _Magic Missile_ memorized. You cast it. That creates a 1/20 chance of something bad happening.
Then, you cast it again: it's now an effective level of 2, so there's a 4/20 chance of mishap. Your third try? 9/20....and your saving throw penalty increases too.
And...you can do this for learning and casting spells too hard for you at your current level, as well.