I found out that you can do double attacks in MMBN 5 DT DS.All you have to do is get in Full Synchro (which is kind of annoying to get especially on bosses) and when it is your turn to pick chips or I think you can do it in mid-battle also,just switch to another person and your Full Synchro for Megaman will go away,but you will do a double attack.

Take Protoman for example when you switch Megaman (while he is in Full Synchro)for Protoman the screen will turn dark and you will do 2xHero or for people that doesn't know what it is,Double Hero.