There's A Beast Inside Us All by @devilishkurumi (Kurumi Shinsetsu-Rei)

“Awww, wazzthe matter, Johnny?” Nny looked back, and his eyes widened as an exact likeness of him appeared, stepping onto Bunny and standing on the small stack of bodies. “Afraid of your inner beast?”

        “Who.... who are you?!”

        “You, of course.  What does it look like?”  The copy grinned at Nny, with a grin that was much too wide to be human, full of inch-long, razor sharp teeth.  The copy waved, showing that his hands were long claws, almost twice the size of Nny’s real fingers.  His feet were cloven hooves, Nny finally noticed, and were not his boots.  “I’m you, Johnny.”

        “You’re not me!  I’m me!”

        “And I’m part of you.  I’m your inner demon.  That little part of you that told you to kill, even after you were free from the Monster’s grasp.  That rotten part of your brain.  But I’m still you.”

^^ "The Beast" from The Idea. Artwork © Copyright 2002 Kurumi Shinsetsu-Rei