OMGYESMAGICSPIKES
-All- magic items cease to work 
Wizards/sorcs/bards/clerics/paladins/druids become near useless 
I think that would be nearly impossible to implement though... All weapons would have to be switched with non-magical ones, as well as every magical item. Then, when everything is over, everything would have to be switched back.
Actually.. after I think about it. I guess it -could- be possible. Perhaps, when a player goes through one of the portals, a script checks all the items in their inventory, and if any of them are magical, it can switch it out with something non-magical but equivalent; e.g. a steel halberd with fire damage could be exchanged for a steel halberd of magic malfunction(without fire damage), and an index value be saved to a character's name( #"Character Name" = 112, 342, 34 ) And, when the event ends, the corresponding item is then returned to the player.
Not being familiar with NWN scripting, that's how I would do it. It would require someone to go through, and list every single magical item in the game, though. Which is quite time-intensive, but doable. There could be a quicker way, [shrugs] but it's not known to me.
