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More specifically, we cancel the Walls of Force from the Material Plane. This will unleash the black hole of wraiths, aka Wraithsun on Material Plane and immediately pull every incorporeal thing in itself. This will eliminate every single incorporeal creature in the Material Plane in a one fell swoop. Only exceptions being things locked inside Walls of Force or Forcecages, which will just be crushed by the huge incorporeal gravity pull.
Now, the funny thing is that since Wraithsun is incorporeal, it won't affect corporeal materials at all. Except for Ghost Touch items, which will be pulled and crushed like they were incorporeal (this might be harmful to anyone wearing a Ghost Touch armour, but we are a wizard, not paladin). Conveniently, this gives us a good grabbing point in the corporeal matter of the Ghost Touch items that we can use to move Wraithsun around.
As a suitably good display of our legendary annihillation of every incorporeal monster, we shall take the Wraithsun to space and have it orbit our planet like a second moon.