Inside Out AU is an alternate universe usually within Rise of the Brave Tangled Dragons universe. In this AU, the characters of The Big Four portray the characters of as the emotions or human characters from Inside Out.
Merida is usually portrayed as Riley Anderson because of her personality. But sometimes she is portrayed as Disgust. Sometimes people portray her as Anger for her temper, passionate attitude and red hair.
Elsa is usually portrayed as Sadness because of her sad back-story and negative personality. This also because of Anna being portrayed as Joy and in Inside Out, Joy and Sadness bond similarly like how Elsa and Anna bond in Frozen. She is also portrayed as Riley Anderson.