Remixes are fun! So basically, authors and artists sign up and list which works they'd be willing to let other artists or authors "remix." Then, you look at your assigned person's works and pick one to work with. You write another work based on the original. Remix writing usually means taking the tropes and applying them to new characters, exploring a different point of view than the one the original author wrote, or making an AU of the fic i.e. with a different beginning or ending; or a different time period. It's pretty open ended, just as long as the new work is different but related. For remixing art, it's a little easier because you can just write fic that is inspired by the art. Sometimes I felt a bit of pressure, because if the original is very well loved it's hard to figure out how to "top it" or do something better. But once I let go of that and just let myself be creative, it became way more fun to participate.