I would like to make it clear that scripts CAN be used in MP, just not via the normal means of attaching them to whatever you want.
In order for MP to use scripts, the scripts MUST be used on weapons. Weapons are required to have scripts in order to function, so those scripts will work. The bad part about this is that they are not always active across the level, and even setting the properties to "Always Active" will not guarantee it to work the same as, say, a trigger zone.
There are also other means of using scripts in MP, via dynamic entities placed in the map while in "Single Player" mode, then swapping to "Arena Mode" before building the game. Remember, though, that for Arena maps, you will need to use character entities instead of a start marker.
Weapon scripts (this paragraph is referring to PB's weapon scripting system) should be functional during MP, same as in SP. If they are not, then that will be considered a bug and should be reported to PB's developer.
The one and only,
