That depends. Would you like to keep the style of your current username or not?
RpNation
Purity
Adorable Monster
Well, if I can yes. If I can't, I will get over it.
Daisie
Use words that sound awesome like nova shadow, shade, wing, ember, stuff like that. 
Purity
I think I'm quite partial to Black Feather, then. Hopefully that's shortened enough.
Adorable Monster
I like those ideas! Hmmm...unique, different, and not something you would normally think of.
Daisie
Supernova is an option too. Or as I said, mix it up and do Black Nova. Or Ember nova.