Is it true that you can simply use a .rel file to port one character over another?
i.e. I want to put Fox over Jigglypuff so that I can put megaman over Fox.
If so, how can I make a .rel file?
Well...I don't think Fox over Jigglypuff would work correctly, from what I can remember, only Ike and Marth can be ported without any glitches, anyway, try this guide and see if it works:
http://forums.kc-mm.com/index.php?topic=46829.0 (http://forums.kc-mm.com/index.php?topic=46829.0)
Thank You