"Creatures of ElfQuest" would be really cool, assuming that it is okay to include elves in the images with the non-elf creatures. Otherwise, it might seem more like a cartoon zoo calendar. (Which sounds cute to me, but maybe not to everyone.) Just need to make sure that it doesn't turn into 12 months of Nightrunner and Starjumper!
"Comedy" strikes me as a potentially daunting theme. Humor is often personal and very difficult to pull off... especially in a single image. A good theme would allow individual creators to strive for comedic images, should they choose, but making comedy a theme might limit participation.
I have mixed feelings on the
"Lesser Known Characters" theme... just on the question of who judges who is lesser known. For example, Jink is "lesser known" to
me, since I never read her series, but probably does not count as "lesser known" to many others. To accomplish something like this, I think one would need a list of characters that could be included or a list of characters that must be excluded. Still, I like the spirit of the idea: featuring characters not normally in the spotlight is a fun concept. As I said, mixed feelings.
The mentions of movies and of different art styles made me think of a theme that may not appeal, but I'll suggest it anyway: ElfQuest crossovers. Set ElfQuest characters in other pop-culture content, like movies or comics... maybe emulating movie posters or something. (The idea needs a little hashing, especially since there is the question of copyright.)