I belong to that demographic of middle-aged mothers who occasionally dabble in fanfiction, and so 'How to Train Your Dragon' has an extra-special place in my heart.
There is a wealth of creativity to be found in this fandom. Two fanfics that I particularly like are 'Becoming Lífþrasir' and 'I Hear Him Scream'. In 'Becoming Lífþrasir', we see what happens when Hiccup is taken in by dragons and 'I Hear Him Scream' is a thrilling and emotional tale of Hiccup, Toothless switching bodies.
Both carry you along on a wild ride and both do this much-loved tale the justice it deserves.