Hi Ghost! I've seen your past contests, but never got the chance to participate in any of them, and I really want to participate in at least one. I do have some ideas:
Cyberpunk Dragons- Futuristic dragons with neon lights
Plant/Forest Guardians- Beyond just a regular Forest, you could make some inspired by swamps, or maybe even "tree" dragons.
Circus/Carnival- Like a clown or a mime.
Skeleton Dragons- its pretty close to the theme of scary dragons AND demon dragons, but I still think this would be cool.
Sea dragons- it could be anything "sea" related, from the top of the ocean to the deep dark abyss, you could do pretty much anything
Seasonal Dragons- Winter, Spring, Summer, and Fall. Pick one of those seasons and make a dragon out of it.
I hope this helped Ghost!