Moderators of the wildly popular VORPG, Polyworld, had no idea that one of their most famous cites Edotown had been stolen and for quite some time. No wonder there were so many complaints and bug reports coming in.
Magic should have side effects, both expected and unexpected - fortuitous and deplorable. Expected side effects add anticipation, while unexpected ones increase the drama of the scene. The result can be comedic or dire, it dpends on which circumstances work best for your game.