It depends on how their illusions work if it would make it impossible for me or not, depending on the character. If they have area of attacks for cheap energy cost they can spam that onto every illusion and hope it's the right one, but if not and they get swarmed by a bunch of illusions and the real one, managing to focus on the real one and defeat them out of the entire group would seem meta gaming so they'd need a way to focus on every illusion coming at them at once.