Self-harm

Self-harm is a major mechanic in The Missing that is both part of the puzzle-solving gameplay, and directly connects to the story. MAJOR SPOILERS will appear after the description of how self-harm relates to gameplay.

JJ has the ability to be grievously wounded and yet recover in a second by holding a button on the controller. This ability first appears early on in the game, when JJ is struck by lightning, electrocuted and then set on fire, before being revived with the apparent help of Deer Man.

Upon getting back up and her body snapping into place, JJ can now regenerate at will after taking damage. And taking damage is something JJ must do intentionally in order to proceed in many cases.

JJ can self-harm, or be injured, in the following ways:

Limb loss and torso severance
After losing a limb, JJ can then pick up that limb and throw it. Limbs can also be used as weights to weigh things down. JJ loses the ability to climb ropes when she has only one arm, and cannot walk with only one leg - instead, she hops for a bit before falling down.

Catching on fire
Catching on fire makes JJ run faster for a short while, before she falls down and collapses. She can also set other things on fire by touching them. If she is injured by a Cymbal Monkey while on fire, she is decapitated. The fire can be put out by water, which disables JJ's ability to set things on fire, requiring her to set herself on fire again. Falling a short distance while on fire will also break her limbs.

Neck injury
If JJ's neck snaps, gravity is reversed. She can lose limbs with reversed gravity, but if she is decapitated, gravity becomes normal, since she no technically no longer has a broken neck due to no longer having a neck. When gravity is reversed, things on the ceiling fall to the floor, including water.

Decapitation
If JJ is decapitated, she can roll around and hop as only a severed head. This allows her to fit into small places that are otherwise inaccessible, and is required for getting some of the trickier hidden donuts. If she takes damage as a head, JJ dies.

Changes in voice caused by injury
If players press the holler button while injured, JJ will call out with a strangled, choked voice. If JJ answers the phone (for voice calls instead of text messages) while injured, she will sound injured while responding, and sometimes even complains about the pain she is in. If she answers the same phone call in a normal state, this doesn't happen, and her voice sounds normal.

How this connects to the story
MAJOR SPOILERS!!!

This is connected to JJ's secret. Being transgender and having a lot of pressure put on her by her mother, in addition to being bullied, JJ may have engaged in self-harm before attempting suicide. However, the game never makes it clear if JJ engaged in any self-harm or not before her suicide attempt.