This was a dream, meaning the real Mark didn't know about the ring yet, or that you were actually a guy. Of course, this version of Mark for all you know, could be your conscience. It would make sense since he was talking to you in a dream, and there was no possible way that he could actually be a vampire under that look during the day.
Finally, Mark smiled, and placed one of his hands on your shoulder. "The ring you have on you doesn't attract goth girls," Mark explains, while he was placing his other hand on your shoulder. "The ring turns you into a goth girl. I mean just look at yourself for a second, and see what I'm trying to say." You look at yourself, and find that Mark was right. You were dressed in black, while you have grown huge breasts, your hips shrank into an hourglass, and even noticed the dark blue hair you have gained.