Lyra Heartstrings wakes up early to the sound of thunking outside her door. When she answers it, she finds Vinyl Scratch trying to deliver her the wrong mail. What's even stranger, Vinyl had Derpy's cutie mark! All five of Lyra's friends have been cutie-switched. They're not themselves anymore. Lyra has to find a way to fix this mess!

Based on this post: http://magicalmysterymod.tumblr.com/post/44124806183/magicalmysterymod-au-with-the-mane-background the concept is all this person's!

Oh, and Octavia is a main character too, but I can only mark five characters and there is not 'mane six background ponies' one :(