My first thought was seeing the dark, red sky, of Pit's sky chase against Dark Pit. That said, I love the colors you chose, I kinda wish they reflected a bit on Dark Pit, though.
But it is a nice contrast. Anyway... Try more dark spots, dissipate the clouds a bit to make their shape more gas-like; if you want to change the background.
Don't chastise yourself, though. Making clouds... is very hard; no matter the medium. Be sure to make a copy of your artwork if you want to experiment.
But, like I said: I'm blown away, this is a fantastic job. Wanna go nuts? Add feather details to his wings. If not; it looks very good and you can be proud.
Sayeth what? Your signature is too small! I had to attempt to download your picture so I could see it bigger. Don't be shy when signing something, Cassi. That's a problem I have as well.
