Yeah, why is it banned? The Mage Association doesn't allow it. Is there something out there I have yet to read that explain why so?
You'd think Reality Marbles aren't such a big deal considering all the super haxs out there that Nasuverse characters tend to have. Considering Magis tend to have many enemies, having a trump card for Magis would be allowed to bail em out. Not much of a Association if many Magis end up screwed and dead.