great work everyone!
and I just noticed that, while it's not quite the triangle trade that happened last time... Hilda cosplayed as Gemini, Gemini as Eagle-Eye, Eagle-Eye as Lentie, Lentie as Hilda.
I like the Battle Trade idea. When people post their info during sign up, they'll probably have to post a bit about their character's skills, abilities, etc. so the artists will know how to portray their "guests".
(also, there will probably be a few... uneven pairings, that will either result in one-sided fights (which could be funny), or perhaps a bit of creative balancing.
the What If? idea may be a bit easier to manage (maybe?), and I think either will be good, but I'm leaning towards Battle Trade-- unless too many people don't like drawing fight scenes.