This fanart here was based on the end of the third chapter when the Dazzlings finally give Twilight their fourth pendant and in the end felt herself changing from a pony to a siren.
Note: I did have a few other fanarts based on the chapters of the story, haven't gotten time to do them yet. So I did this one just for context. If you'd like me to do the others let me know.
The fanfiction can be found right here: Twilight Becomes a Dazzling — Fimfiction