"So, who're you gonna shoot?" Mary pointed the big, fuck-off gun at the midpoint between her two choices of target. She stood between them and the door, and of the three people in the room, she was the only one who looked unique. The other two were perfect facsimiles of each other.
To be precise, one was the facsimile of the other. A demon of the old world, forgotten by cultures grown skeptical of such terrors, released by her brother's stupidity.
"C'mon, sis," whined her brother or the brother-thing. "If you don't shoot it, it'll destroy the world. Shooooot iiiiiit."
"I'm not the it," said the other. "I can prove it. Remember when I read your diary when I was eight? Well—"
"Of course you remember," the first sneered. "You stole my memories with my body, you monster."
"I'm not the monster, you are! Please, Mare, it's him. Shoot it. Please?"
Mary looked at each for a long moment, unable to to find even the smallest discrepancy. "You're forgetting something." Both canted their heads in the same confused way. "I never liked my brother. Besides, the needs of the many, and all that." Their eyes widened at the same time.