Corrupting magic.

[Pyrex]

The essential problem is that spellcasters are expected to cast spells, and lots of them, over the course of their career. Giving them a chance of acquiring a permanent penalty each time they cast a spell with no mitigation leaves them at "doomed".

For example: What would it do to your average Fighter if they injured themselves and lost 1 permanent HP each time they rolled a natural 1 on an attack roll? --> They'd be doomed.

As a rough average, we can safely assume that a primary-caster character will cast approximately Level*13 spells at each level (13 spells from 1->2, 26 from 2->3 on up to 260 spells from 20->21) for a total of 1365 spells across their 1-20 career (including their time spent at 20th level).

With a 5% chance of acquiring taint per cast, your average caster will accumulate ~70 points of taint across their career. More if their chance is higher than 5%. Much, much more if their chance increases based on their taint score.

 

[Aurora]

Gonna have to agree with Pyrex on this one. Why play a spellcaster if I have a chance of becoming evil or losing my mind every time I cast a spell? I can understand saying if you cast alot of evil spells- you will turn evil, but other than that, I would complain as one of your players. JMHO.

 

[Primitive Screwhead]

The first thing I would suggest to do with this system {if my DM was adamanant that it fit the setting and refused to run another setting...and I didn't want to run a game } is..

Divorce the chance to earn taint from the effects of taint. As Jack Smith noted above it should be level independant. Basically have spell casting require a save, failure increases Taint. Perhaps even as simple as saving against the spells normal DC.

Then develop a scale of taint effects that start light and then build either in numbers or in severity. Ravenlofts rules seemed pretty good for this. One key is that the character needs to have a way to 'beat the odds'.. there should not be a lethal result to casting spells.

Each level of taint would have to be balanced.. you said "...having fits when trying to cast"
as an example of a 'light' affliction. Not too sure but I am sure having fits mid combat could be a bad way to go. Try to avoid effects that remove the players control of the character and stick to ones that impact the characters capabilities.

To be playable you need to turn the flawed, unfair concept into some good, fair mechanics...and there, as they say, is the rub

 

[Jack Simth]

Something else you might consider:

Taint is social only.

Each spell has a chance of increasing your taint score. Taint causes essentially harmless minor mutations on the skin. The more taint, the more mutations.

People get a spot check, say, DC 30-Taint score, to notice that you're tainted. Anything that would change a person's appearence gives a bonus to the DC/Penalty to the Spot for the duration - perhaps based on your Disguise check.

The most commonly known source of Taint is spellcasting.

Spellcasters are a hunted species.

And there you go! Cast overly much, and you'll have to avoid civilized areas. To get basic supplies, you'll either need to be separated from the party (dangerous, that) or carefully disguise yourself (magic a bad idea, as it has a chance of increasing your Taint).

 

[NATOCM]

After buying a copy of blight magic and reading the relevant parts, and your very good and helpful advise, here is v2. I’ve decided to go with Taint points and “The Taint”, because it sounds cool ((also, sorry if it doesn’t make sense, its quite late and I know if I don’t get this down it’ll be gone by tomorrow morning)):

All Spell casters are affected by “The Taint”; the corrupting effect of magic when used to excess.

In IC terms the tapping into a pool of ancient power formed when the creator god exterminated a long dead, and highly magical race. The powerful religious leaders of this world view the practise of any form of magic as extremely heretical. Not only is this a political and social issue, but also the extended use of magic results in “The Taint” manifesting and corrupting the users body and mind.

Effect of “The Taint” on core rules
The effects of “The Taint” on the game mechanic are small as the results are mainly role-play orientated. The concept behind “The Taint” is to make magic less appealing, while opening up role-play opportunities. However in the later stages of “The Taint”, considering with the use of high-level magic can result in more extreme effects and hence the editing of core rules by “The Taint” is unavoidable to maintain the effectiveness of the deterrent over higher levels

“The Taint” and Taint points.
Taint points are the basis of “The Taint”. How many Taint points you have determines your level of taint and how it affects your mental and physical well being. You cannot gain any taint points bellow spell caster level 5 or gain more than twice your spell caster level of taint points. Removal of taint points is imposable save the use of Wish or Miracle spells and Devine Intervention, however it is not possible to remove all Taint from your body, All spell casters will retain at least one.

Gaining Taint Points.
Whenever a spell caster of any kind successfully casts a spell of level 5 or above they must make a Taint Check: D20 + Will + Spell caster’s primary Attribute.

The DC for this is: 10 + Spell level + Current Taint points.

If the check is made then the Character suffers no effect. If they fail they gain a taint point.

The effects of Taint points
Every a character gains a spell caster level they must D12 roll on the Taint affects table. There is an individual table for each level and each table comprise of 10 possible effects and 2 level modifiers, 1 is always roll as level bellow, 12 is always roll as the level above. The effects range in harshness from 2 to 11 in each table. In other words the lower your roll is the better it is. If you obtain the same effect twice then re roll from your starting level ((For example, if I’m level 10, and roll a 1, I would roll again on the level 9 table. However if I roll a duplicate of something I already have, I roll again on the level 10 table))

I don’t have the tables yet, but I am not thinking of having any major rules changing effects before level 15.

Thanks for your help and I hope this isn’t too confusing!

 

[Pyrex]

Could you explain the Taint check a little better? I'm assuming you mean d20 + Base Will Save Bonus + Spellcasting Attribute Bonus, but that's not entirely clear. It might be easer just to give in and make it a will save. Sure, it favors Divine casters a bit, but Wisdom is typically a better attribute to use to resist taint/insanity/whatever anyway, so...

Assuming that's what you had in mind, the value of the Taint check is going to converge to approximately d20+Caster Level for single-class characters (Base will save is 1/2 level +2, Attribute bonus starts off high, and increases slowly, arriving at around +10 for 20th level characters).

Again, the problem of the DC rapidly increasing is still present; as not only does casting higher-level spells increase, the DC, but each failed check increases the DC by one.

I'll try and post an analysis later, but your average caster is going to fail 2-3 checks getting from 1st to 2nd level, and my guess is he's doomed* around 6th level.

*Doomed in this case being defined as having a large enough taint score that succeeding at subsequent taint checks is impossible.

The linear DC increase absolutely has to go if there is no way to eliminate taint.

Here's an alternate solution that might preserve your flavor of Taint never really going away but not becoming quite as overwhelming either.

-----

First we take a page from Mage and treat Taint as a fluid attribute. As above, you make a taint check each time you cast a spell and accumulate temporary Taint, increasing the DC for further checks.

When a failed Taint check increases your Taint score to >2*Caster Level, your Taint score is reset to 0 and you gain a Taint Flaw of level equal to your Caster Level

 

[Storyteller01]

Something else you might consider:


Spellcasters are a hunted species.

We actually did this for clerics. The rulers didn't like the gods, and what not. It worked out really well.