Dark AU

Dark AU (also known as the Evil Four) is a popular AU (Alternate Universe) within the Rise of the Brave Tangled Dragons fandom. In the AU, Rapunzel, Merida, Hiccup and Jack Frost are all changed into darker versions of themselves. Because it is not canon, ideas for this AU are shown through fanfiction, fanart, and other fan-made works.

About the AU
In some fanfics, Jack Frost from Rise of the Guardians, Merida from Brave, Rapunzel from Tangled or Hiccup from How to Train Your Dragon  are changed into a dark version of themselves, usually by Pitch Black. This may sometimes cause much conflict and destruction among the members of the team.

Some fans also indicate that the Big Four run into dark counterparts of themselves.

Hiccup Horrendous Haddock III
The Dark Spirit of Betrayal, supposed to be Guardian of Change, Element of Earth, and Spirit of Autumn. Out of all the Big Four, Hiccup's place in Dark AU has been explored the most. The most common scenario portrays him as simply a victim of prejudice for the sake of his dragon and branded as an Outcast by his tribe, leaving him bitter and vengeful. Other cases show that the loneliness and alienation inflicted on him by his tribe and his father left his mind in a fragile mental state, leading to murder or some degree of sadism to those who would be considered his friends and family.

Jack Frost
The Dark Spirit of Mischief, supposed to be Guardian of Fun, Element of Water, and Spirit of Winter. This darker incarnation of Jack Frost is usually portrayed as the comedically named Jack Black.

Merida DunBroch
The Dark Spirit of Chaos (or Misfortune, supposed to be Guardian of Courage, Element of Fire, and Spirit of Summer.

Rapunzel
The Dark Spirit of Doubt, supposed to be Guardian of Creativity, Element of Air, and Spirit of Spring.

Fanfiction

 * The Final Four by DisneyDame88
 * Extinguished by DisneyDame88
 * Random Evil Big Four Drabbles by randomobsession123