This was by far the easiest to 100% by a country mile.

Technically speaking I've 100%ed, but I haven't caught all the fish in the fishing hole but that's so hard to tell when you've completed so I'm giving myself this one.

I haven't played every level with Mario and Luigi, but the save file is glowy so I'll count it (and its not like it keeps record of which levels you've played with which character)

Completed the main campaign on professional, Separate Ways, Assignment Ada and all of Mercenaries 5 stars all maps.