What if your reflection is not actually you, but in fact it’s a demonic creature watching and waiting. Each time you visit the mirror it get’s stronger, it learns better how to mimic you, how to be you. When it’s ready it will emerge from the mirror devouring you and taking your place. - Creepy spooky stories to give you nightmares
"I am here for you." The words left his mouth and he meant them. She threw herself at him taking him in her embrace and pierced his abdomen with a small knife. He stumbled back after the blow and looked into his loves eyes that held nothing but blackness. He let his own darkness take over and flew up in the sky looking like a demon. Although looking like a demon he had a broken heart.
In worlds that Chaos conquers the Phase energy becomes corrupted. This corrupted energy will often become these things, commonly called Chaos creatures or Corrupts. When these creatures are 'killed' their energy cycles through the Phase again and becomes uncorrupted. In order to reclaim a world from Chaos all of the creatures must be destroyed.