This is a character design my boyfriend and I have been discussing for a while...
Basically, due to some RPs we have done in the past, I came up with an original design for a (humanized) "Nightmare" Cadance. The design is partly inspired by a piece of artwork of Nightmare Cadance called "Bleeding Heart", found here: http://russiankolz.deviantart.com/ar...eart-335545192
Essentially, my idea is that this is what would have happened to Cadance if the events at the beginning of Season 3 went differently--what if Spike wasn't able to get the Crystal Heart to Cadance in time? What if she had been completely exhausted of her magic?
And most importantly, what if being completely exhausted of her magic had left her vulnerable to be "tainted" by Sombra's shadow/fear magic? What if his magic twisted hers somehow, made it darker, more... primal? What if, instead of being a bearer of love and light, she became a beacon of darkness and passion?
I've already got plans to commission a red/silver version of Cadance's cutie mark, though mine won't have the thorn motif that the design above has. I'm going to get the Candy Striper from Arda in Melody, which is based on Cadance's mane, and darken the color with dye so that it isn't so light/bright.
The biggest decisions I still need to make are for the outfit itself. Whatever I do, I want it to be still recognizable as Cadance but twisted somehow. I'm thinking dark reds and purples such as the colors used in the image above, rich fabrics like brocades and silks, with plenty of black as well. I'm a bigger girl, so I want to emphasize my better assets (my chest) while minimizing my not-so-good ones (my stomach/thighs), so I'm planning to make a corset or cincher for the costume. I'm considering going with a burlesque-style outfit with the cutie mark on the corset or the skirt.
EDIT: another piece of artwork that is inspiring the design: http://cuttycommando.deviantart.com/art/Lust-342677087