I'm going to be creating a new FIM rewrite, but the mane 6(same ones as in the mane show) will be monster-ponies
Rainbow will be a tatzlpony

Rarity will be a spider-pony

Applejack will be a timberpony(Timberwolf + Pony)

Twilight will be a lamia

Pinkie will be a changeling

and Fluttershy will be a bat-pony(image was best I could find)

Like if you support this and comment your thoughts