@S121
I think it's a fitting weapon for John and whenever he does get it, it will serve as a reliable weapon. Also when Pandora is opened it damages all enemies in a flash of violated taboo. (In other words really freaking powerful surge of energy.)
The forms:
PF013: Epidemic:

Pandora transforms into a powerful bowgun that fires ravaging projectiles
PF124: Hatred:

Basically a triple Rocket Launcher
PF398: Revenge:

Pandora transforms into a powerful cannon that fires searing blasts of energy at opponents.
PF262: Jealousy:

Pandora transforms into a Gatling gun to rain down a hail of hot lead upon opponents.
PF594: Argument:

Pandora transforms into a mobile missile battery that fires a barrage of homing missiles.
PF422: Grief:

Transform Pandora into a boomerang and use it to slice through enemies.
PF666: Omen: Open Pandora to damage all surrounding enemies with the flash of a violated taboo.
Pandora uses something called the Disaster Gauge which is filled upon successful attacks with Epidemic, Hatred, Revenge, and Jealousy.
Argument, Grief, and Omen all use energy from the Disaster Gauge. Omen uses up all Disaster energy meaning Pandora has to be at max power to use. Argument just has to have half of the Disaster gauge to be used, but is more powerful if the gauge is full.
Grief uses up 25% of the Disaster Gauge I think.