The most up to date version of this contest's rules is at https://www.fimfiction.net/group/217156/portal-transformations/thread/529551/portal-transformations-contest-announcement-and-rules. Please ask your questions there.
Welcome to the Contest
"When Spike goes through the Mirror Portal from Equestria to CHS, he turns into a dog. What does X turn into when X goes through the Mirror Portal (or a similar portal)? You can pick X and the direction."