A demon.
Katie watched in amazement as Tiff's skin turned a dark shade of red like the color of blood. Tiff felt pressure building in her head like a really bad migraine was hitting her and she tried applying pressure to it only to feel her horns grow until they were were four inches long and were a jet black. Tiff dropped to her knees and grabbed her stomach as a great emptiness left her drained of energy. Her nail's lengthened to an inch long and also turned black. Katie thought it was really cool as Tiff's clothes changed from a white t-shirt and jeans to black leather hot pants and a halter top that reminded Katie of Catwoman from that movie. This only emphasized her prominent breasts which had been nothing to sneer at before but were a now a firm DD. Tiff gasped as she felt black leathery wings growing from her back and her shoes turned into 6" stilettos.
Tiff stood up and looked into Katie's eyes with her red eyes. Katie watched in fascination and horror as Tiff's black lips parted to reveal white teeth that almost seemed to shine and really drew attention to her prominent fangs. A forked serpent's tongue flicked out before disappearing back in her mouth. Katie looked around for the ray gun, frantic after seeing what had happened to her friend. "I'm sorry Tiff. I didn't know this was going to happen. I'll find the ray gun and change you back as soon as possible."
Katie was shocked when Tiff grabbed her wrist and applied so much pressure that it felt like it was going to break and Tiff's nails were digging into her flesh allowing a small trickle of blood to flow out. "Tiff, what are you doing? You're hurting me."
Tiff bent forward and licked the blood coming from Katie's wound. Katie was shocked as she felt a rush of ecstasy follow the action so that she was feeling weak-kneed. "Katie, I don't want to change back. It's always been a wish of mine to be desired this way. To be irresistible and now I finally am. Now that I have it I'm not going to throw this opportunity away. As for you Katie, you're mine now and you'll be begging to be with me from now on after what I do to you. Trust me, this is the fun part."