Pandora's box is an artifact from which you can receive either a positive or a negative buff. They can be found in multi-player dungeons and solo campaigns.
For level 60 and more multiplayer dungeons (MPD's) it only gives positive buffs (?)
Random statistics enhancement or hindrance, like:
PDEF +1 ~ +10 hindrance
Health + 250~ -850 hindrance
Rage Boost + 50
MATK + 5