There seems to be an unused enemy sprite. I have NEVER seen this before, so.. yeah.
(http://img195.imageshack.us/img195/7086/unusedenemysprite.png)
However, here's the interesting thing: all of his animations are similar to Fusion Dragon's!
Perhaps when the editor is more advanced, we could add him in as a decently powerful optional boss. But what could Camelot have had in mind for this creature? He seems to be some kind of chimera, or perhaps he's something else entirely. We may never know.
Umm... yes, there's TWO unused enemies, and both are talked about in another thread. Feel free to make them USED enemies via the editor, though. Probably not as a boss, though. They seem too generic. Well, granted, the one you posted may have one of its forms as a boss, sure (look at the Hydra and Gorilla type monsters for example). But still, nothing too major.