You have been chosen. The criteria of this selection are as vague and mysterious as the selection process itself. One day, there was a flicker in the window, or was it a puddle, perhaps a mirror? Something was there that didn't belong, a trick of the mind perhaps, had it not been persistent. Everywhere you went, he followed; man within the reflection, staring. Soon it wasn't a problem of sight, but of hearing too. A grating sound that penetrated the depths of the mind accompanied his appearance. It stopped as abruptly as it began, the sound that is. The man still stood there, staring into your eyes. Without any intelligible reason, he spoke. It sounded as if he stood just behind you, but a quick glance revealed whatever scenery you occupied.
"You are chosen. There are others like you. Only one can survive."
Like that, he was there, behind you, piece of what looked like plastic in his hands. Any attempt to interact with him, was met with silence, physical contact seemed impossible, as he disappeared the moment he was touched, appearing just out of vision.
"Accept it. Fight! Until only one stands!"
Upon taking the plastic from his hands, a flash of light would blind you. Upon clearing, the others he referred to would stand before you in a hall of mirrors.