The Fearless DM

In my upcoming Labyrinth Lord campaign, magic is known to be a warping and destabilizing influence. Each time a spellcaster casts, he rolls a 1d20, and on a critical fail (a roll of 1) the spellcaster will begin to develop a mutation of some kind.

These mutations are not powers! They also don’t happen immediately. The only immediate manifestation will be a nosebleed (or something similar).

Within a few days the PC will change- sometimes subtly, and sometimes in more extreme ways. Eye color (in one or both eyes) might change as a subtle effect.. warts or carbuncles could appear. At the far end of the spectrum (high level spells might cause more dramatic effects) the wizard grows more monstrous, developing an extra eye, or even growing eyestalks or feathers, or becoming grossly fat. The highest level wizards learn to polymorph, and the most evil are able to transfer their infirmities into the bodies of a captured victim, or their minds into new bodies.

Therefore, it’s not a “low-magic” setting, but it is a setting where magic is not treated lightly… and nobody trusts a magic user.