Something is going horribly, astoundingly wrong at the home of Mr. and Mrs. Claus. Gingerbread men rampage through the kitchen, leaving a bloody mess. The television blips in and out while “Rudolph the Red Nose Reindeer” plays on the screen. Demonic elves decorate Christmas trees with skulls. But it’s all in the name of horror and fun at 13th Floor’s Krampus haunted house. The 13th Floor has become a Denver institution during October with people waiting in long lines to get spooked, but the demand for scary fun is expanding in the city and across the United States as Halloween grows in popularity. “People in general are looking for Halloween year-round,” said Samantha Beranek, a 13th Floor spokeswoman.