Speed demon
Basically a gambler but for movement speed.
The lower your health is the faster you move. It can be incredibly balanced by his own design since you risk to kill your self costantly at higher speed due to fall damage.
For the sake of balance (and fun) it should make you 1% faster per each point of HP missing
Or, for the sake of semplicity. Once you pass the 50 HP threshold you gain 2% movement speed per HP point missing.
Imo it shouldn’t have any side effect other then increased recoil (make sense, you are going really fast)