Originally posted by lemon
It might be something like this
Teddy bear: 0% chance, increases 5% every time mystery box is used
BAD weapon (Pistols, rocket launchers, sniper rifle, etc): 60%
GOOD weapon (RPK, HK21, AUG, Monkey bombs, etc): 30%
AWESOME weapon (ray gun, thundergun, etc): 10%
But I really have no idea =D