I'm assuming your game is pretty low level, or your spellcasters don't have the right spells or haven't grasped the concept of the nightmare you are setting yourself up for, because when they can cast 4th+ level spells without concentration, there will be no way to stop a wizard. Just off the top of my head alone, I would create a nightmare senerio with greater invisibility, fly, and haste. No concentration, no fear of spell failure, there will be no way to dispel or counter anything I do.
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