Our Babysitter is a Ghost?!?!?

Danny Fenton can never get a break. Of course, even when he thinks he does he doesn't. Going to Gravity Falls was supposed to be a way to relax, but with having to work for his video game coupled with having to babysit twins who attract just as much paranormal activity as he does. Not to mention that anarmy has been created out of ghosts who want nothing more than to pulverize Danny and take over the world. But who's the mastermind?