Nox Castle would be good (I think that's what it's called), where you control Daein forces trying to hold the line against the Greil Mercenaries. It was home to a fairly epic battle involving a ton of Laguz and Daein soldiers. It could be a large level where the two sides of the armies come and randomly fight each other, potentially catching smashers in the crossfire. (Edward, Leonardo, Micaiah, Nolan, Sothe and some other members of the Dawn Brigade could make appearances and attack the Greil Mercenaries (Soren, Mia, Shinon, Ranulf, Mist, some Laguz and maybe some others). Then to make it even more epic, the Dragon Laguz can show up and destroy part of the castle like they do at the end of the level.