I've wanted to do a "Smash but every character gets exactly one home stage" roster for quite a while, but the one thing standing in my path has always been Fire Emblem. I was thinking of assigning "Others" stages to FE, but other than Golden Sun and maybe an AR Games Dragon stage I don't think there's any that fit. (I'm not using Streetpass Quest. It's a fun reference but god it looks visually bland.)
Shoulda looked up the Boss Battles thing myself, though - sorry.