When you are taken to exactly 0hp, you get a Scar. Your first Scar adds d6hp to your Maximum.

Scars only occur in deadly situations, not training.

Roll d6 plus the damage caused by the attack
2Busted FootReduced to a limp until fixed.
3Lasting PainA nasty scar that causes intense pain if pressed on.
4Busted LungYour breathing is loud and you cough up blood often. It’s gross.
5Smashed JawYou lose a lot of teeth and get a speech impediment.
6Bloody MessIt needs lots of Stitches, and you don’t benefit from Resting until it’s done by a someone who knows how.
7Shaken NervesYou stammer, twitch, or shake, unless you use something to calm your nerves.
8DisfigurementThe injury leaves your face totally disfigured.
9Mind SplinterA specific element of this injury is stuck in your psyche. Lose d6 Intelligence each time you're forced to confront it.
10Gouged EyeA random eye is gouged out.
11ObsessionDo not benefit from rests until you achieve revenge.
12Hewn LimbOne of your limbs (1: right arm, 2: left arm, 3: right leg, 4: left leg) is torn off or in need of amputation.
13Terrible FractureA random limb (1: right arm, 2: left arm, 3: right leg, 4: left leg) is broken in the worst way. It can be set by someone who knows how, but until then you cannot use it, or benefit from Rests.
14Lost SenseOne of your senses is lost (1: Sight, 2: Hearing, 3: Scent, 4: Taste).
15Heart DamageThis vital organ is in critical state. If you suffer this Scar again, you die.
16Shadow of DeathYou feel a cold hand on your shoulder and have nightmares. Any time you sleep, pass a Wisdom Save or scream through the night.
17Fractured SkullYou drool and slur. If you suffer this affliction a second time your skull is utterly split open and you die.
18+Doomed to DieYou shouldn't have survived that. You have nightmares of your own death. If you fail your next risky Save, you die horribly. If you pass, remove this effect.

Credit: Adapted from Chris McDowall's Electric Bastionland.