I think it would be awesome to have [i]all[/i] the friends. Have every student PC currently in the dining hall fighting as one group. I think that could work.

I would also propose a slight variation on how we normally write collabs. Normally, we each just submit a paragraph or two (perhaps more depending on the circumstance) explaining what our character did and thought, and that is fine. However, for fighting, I think it would be better to all write the same paragraph, essentially. We give an action, then have each of our characters responses to form a paragraph. I think it would make it more connected, with greater potential for cooperation between characters.