First off- to all those who have suggested a thaumaturgy weapons-grade spell... this assumes PERMANENT brain damage, which I explicitly stated not.
The idea that brains don't heal is... well, a myth. Brains are highly adaptive and heal, but slowly. Examples follow.
My primary concern has to do with the consequences taken. The primary consequences available to everyone are P/M/S, but many others aren't... so what consequences are available to the player matter. Also, flavor matters. Some brain damage causes physical disability... some brain damage causes mental issues. Examples also follow.
There was some testing a while back where a group of test subjects were asked to wear prism glasses that completely inverted everything they saw. At first, they really couldn't cope... but after a couple weeks, they all reported something odd- the world was back to being right-side-up... their brains had adapted to invert the images again... and now the world was upside-down without the glasses. When asked to remove them, it took another couple weeks for the brain to re-rewire itself to adapt.
I'm a synesthetic... in particular, most of my senses are linked to my sense of touch, due to a my brain never having properly trimmed all the boatloads unnecessary neural connections it formed as a baby.... in particular, it's a little faster at forming new ones, and a little slower at trimming them than anyone my age. Most people with synesthesia learn to cope with it fairly easily in time... but as they age, it's also possible for the synesthesia to fade. I used to have a strong pain response to a particular stimuli that's since gone away. I'm not sure whether synesthesia would qualify as physical or mental, but I'd barely lean towards mental, myself... and it can definitely be caused by rewiring someone's brain. Hell, LSD causes short-term synesthesia.
I used to work with a man (as his caretaker) who had moderate mental retardation and aphasia. Aphasia I would ABSOLUTELY qualify as a mental disorder- so does medicine and psychology. It's similar to synesthesia on a lot of fronts, but instead of a scrambling of the sensory centers, it's a scrambling of the language centers... and while my guy was born with it, it's possible to develop... and possible to recover from. Those who recover typically do in one of two ways- either their brain fixes it's own miswiring (like with the glasses), or the person can relearn english as a second language. Even my guy was able to do this latter to some degree, if never completely (on account of his mental retardation). I'd call this a textbook Severe consequence, and most likely Mental.
And if it's only a severe consequence, it would probably land squarely in the grey zone of the laws... just like almost killing someone with magic doesn't count as a 1st law violation.
That said... I only barely lean towards this being able to cause mental damage... mostly because mental damage is supposed to be rare.... and the last thing we need is another way for someone to legally completely bypass all toughness. As such- I'm easily convinced to call it physical and avoid the issue, but wanted to touch base with the forums first.
Radijs/SunlessNick- does this make my question a little more clear?
newtinmpls- of course it's probably evil- it's certainly very very vicious, and it takes a certain kind of person to be that vicious... 99% of the time... not someone good.
TheMouse- I didn't think of 4th law... I like that.
sinker/zenten- thanks for the input
jb.teller4- that was more than just 2 cents... and I appreciate it.