There are no guidelines as such but there are two categories. Journal Fiction is writing in the same style and length as the Myth 1 and 2 journal entries to describe an event which we know and heard about but the Journal Writer did not experience personally. For example the last battle for Bagrada.They should be as historically accurate as possible and may require a lot of research and will be judged by the staff here for quality.
The other category is Other Fiction. This is anything else basically. Judging by your description, your piece would probably fit into this category.
If it's a parody then there's also the Parodies of Myth section and for artwork there's the Myth Art section. I hope that helps.
When you're ready, send them in to me and I'll sort you out.