I'm planning to build a random list of characteristics for magic-users in my upcoming game. Since my setting sees magic as a violation of reality, the first time a user casts a spell, they get a permanent mark of some kind. I'm hoping to get the list big enough for a d20 roll, with possibly a 20 result forcing two rolls. I'm gonna put up what I have so far, and hopefully you folks can come up with a whole bunch of cool ideas for me to leach off of.

Some guidelines:
1) It has to be obvious in some way.
2) It may be possible to hide it, but it can never be gotten of. Feel free to add some appropriately flashy means of the mark coming back in short order if the caster tries to get rid of it.
3) It can't prevent the caster from using their spells
4) If it could possibly do damage, it can do no more than 1 point.

So here's what I have so far.
   1: The casters skin turns an unnatural color for their race.
  2: The casters eyes glow. The light is bright enough for the caster to read by within 2 feet.
  3: The caster’s hair is abundant and reaches the waist. If it is ever cut, the hair re-grows itself within 5 seconds and the cut hair turns to dust.
  4: The caster’s hands age in reverse. For an older caster, they are young and smooth. A young caster’s hands are wrinkled and spotted.
  5: The caster smells noticeably of sulfur.
  6: The caster grows horns or antlers. They are not sharp enough to cause much harm to others (1 point damage only).
  7: The caster’s tongue becomes long and forked like a snake. The casters voice becomes sibilant and can easily be seen when spells are cast.
  8: The caster gains a third, sightless, and unblinking eye in the middle of the forehead.
  9: Cool smoke flows from the caster’ mouth and nose when he exhales or speaks.
  10: The caster’s body suffers from random and unavoidable tics and twitches. It does not affect the caster’s ability to cast.
  11: The skin is abnormally cold or hot to the touch. While it can be felt at a distance, only prolonged and direct contact could cause any lasting effect (1 minute exposure has 50% chance of causing 1 point of damage).
  12: Whenever the caster moves, a faint sound of chimes or bells can be heard. It can make moving quietly difficult.
    13: Mist is always gathered 2 feet about the caster’s legs and feet.

You might get some things from my table 'Effects of Powerful Magic on the Caster', in this section of my tables site.

A superb list! I knew there would be at least one other list to peruse for inspiration.

Edit: Damn, I knew I was inspired to put up my own list from somewhere, I read Grognardia regularly.

Thanks

14: The caster floats about 6 inches above the ground. This does not affect their movement in any significant way.
15: The casters' eyes turn completely one solid colour. If they already were one solid colour, they become patterned.
16: The caster carries an aura of fear, disturbance or disquiet. Others are never quite comfortable around them.
17: The casters' features are obscured such that they can never be recognized by facial features. However, they must always wear the same, distinct clothes as they wore when they cast their first spell.
18: The first sentence the caster speaks when starting a conversation will always be spoken backwards.

ooh, those are good Narf. I especially like 16 and 18.

I did add a new one I'm sure I want:
The caster becomes a hunchback.

Hunchbacks are weird.

...I'm quite sure an actual feature of real people would be in bad taste.

Quote from: Narf the Mouse;272602...I'm quite sure an actual feature of real people would be in bad taste.

It's not really meant in bad taste, though if my group found it offensive I'd drop it no questions asked. It's just a way of showing how using magic to shape reality against its own rules will cause reality to shape you back and make you different than everyone else.

I'd probably drop it if I have even more inventive oddities to replace them with.

List as of right now:
        1: The caster's skin turns an unnatural color for their race.
 2: The caster's eyes glow. The light is bright enough for the caster to read by within 2 feet.
 3: The caster's hair is abundant and reaches the waist. If it is ever cut, the hair re-grows itself within 5 seconds and the cut hair turns to dust.
 4: The caster's hands age in reverse. For an older caster, they are young and smooth. A young caster's hands are wrinkled and spotted.
 5: The caster smells noticeably of sulfur.
 6: The caster grows horns or antlers. They are not sharp enough to cause much harm to others (1 point damage only).
 7: The caster's tongue becomes long and forked like a snake. The casters voice becomes sibilant and can easily be seen when spells are cast.
 8: The caster gains a third, sightless, and unblinking eye in the middle of the forehead.
 9: Cool smoke flows from the caster's mouth and nose when he exhales or speaks.
 10: The caster's body suffers from random and unavoidable tics and twitches. It does not affect the caster's ability to cast.
 11: The skin is abnormally cold or hot to the touch. While it can be felt at a distance, only prolonged and direct contact could cause any lasting effect.
 12: Whenever the caster moves, a faint sound of chimes or bells can be heard. It can make moving quietly difficult.
 13: Mist is always gathered 2 feet about the caster's legs and feet.  
 14: The caster is hunchbacked.
 15: Caster is wracked with a incurably phlegmatic cough.
 16: The first sentence the caster speaks when starting a conversation will always be spoken backwards.
 17: The caster's nose rots off, leaving only two slits on the face.
 18: The caster's hands and feet become webbed (at least he's a better swimmer?)
 19: The caster grows a slender hairless tail three feet long that ends in a dart-like shape.
 20: Roll for two different marks and keep both!