Oof, I think I'll stand myself out of this one. [...] but I don't read nearly enough of what is popular in fantasy currently.
Please don't. It's not a rule to use characters from bestsellers and using somebody cool from a lesser known book/series may even get some people to read that book.

Bouuuuh I don't want to not participate but I hate fan fiction... 
I'm not a fan either - at least that's what I thought until I read some entries of the last fanfic contests. Fanfic can be cool.

My voice just won't fit other people's creation. Just dreaming up situations feels wrong and out of context... 
See it as a challenge to your writing abilities.

I know that writing fanfic is hard - especially if you try to emulate someone else's voice. Having a crossover theme this time makes it easier I think, because it doesn't have to take place in another author's world.
Comic books do it constantly (Marvel vs DC; Mickey Mouse vs some real historical persons, ...) and it works great there.
Shout-out for @ScarletBea who is an incredible help with the contests and helps me immensely with staying on schedule (except with the publication of the winners on the main site - we're working on that)!
Wanted to Like that ........................
Please do.

I'd prefer if we stayed with book characters, after all this is mainly a book site, but I'll leave it to xiagan to set up the rules 
Completely agree. (Besides, having more options to choose from makes it even harder.

)