This is the Rise of the Brave Tangled Dragons crime au where the Big Four, and other characters in the fandom, are people who solve or commit crime, like thieves, mobsters, detectives and even spies. (takes place in modern time)

Hiccup: a hacker.

Jack Frost: a crime consultant.

Merida: a kick-*ss detective.

Rapunzel: a spy.

Hiro and Tadashi: thieves living in the streets. Tadashi's thief name will be Kitsune and wears a Kitsune mask to hide his identity.

Elsa: police detective.

Adrien: a thief due to his black cat-persona.

OCs:

Ursula: homeless thief.

Scarlet: a kick-*ss detective.

Sapphire: daughter of a billionaire, but she has a kind and gentle personality.

Wendy: an amateur detective with Violet Parr.