About the AUEdit
Spawning from fanart, this AU places the Big Four, and other such characters in the fandom, as characters from the Scooby-Doo franchise, most commonly as the five members of Mystery Inc.: Fred Jones, Velma Dinkley, Daphne Blake, Shaggy Rogers and Scooby-Doo.
Because of all the "monsters" that are shown (and unmasked) in the franchise, fans like to consider this AU an alternative to Monster AU.
The Big FourEdit
To compliment Toothless, as well as his shaggy brown hair and affinity for green and brown, Hiccup is often portrayed as Shaggy Rogers.
Most people depict him as Fred Jones, the leader and trap specailist of the group.
Merida's role is tricky. Some cast her as Daphne Blake due to her red hair whereas, others portray her as Velma Dinkley because of their similarities shown with the colour orange.
Much like Merida, Rapunzel could play either one of the girls. When shown as Velma Dinkley she usually has her hair cut short and brown like it is at the end of the movie. While as Daphne Blake she has her long blond hair.
As the "fifth member" of the Big Four and animal companion to the group, Toothless is often portrayed as Scooby-Doo.
Due to Robert Callaghan being a masked villain that was defeated by a group of teenagers, as well as taking on the persona of a spirit, "Yokai" can easily serve as one of the "monsters" that Scooby and the gang unmask and bring to justice.