I have a small suggestion, but it looks like it probably won't get in. It'd still be awesome if you could do this though.
http://www.youtube.com/watch?v=Wedc9fc5lhg
This is a vid I made with some random ideas for Megaman in Brawl, skip to 1:44 and read the info about the "Shield Arm" from MML2.
Or, just read this post.
I was thinking his down special could be the MML2 shield arm, which ABSORBS energy projectiles (like pit's arrows... or anything else Lucas/Ness can absorb) but not normal things thrown at him like a bat. (Those will still hurt him).
Also, a small thing not to many people know about MML2, is that the shield actually can be used to attack. The sheild has small white dots that float on the outside of the shield moving to the top middle. The more attacks you absorb, the bigger those dots get. When you release the shield after absorbing enough energy, it lets out a shockwave all around it. It looks bigger and does more damage depending on how much energy it absorbed. And in MML2, Trigger is able to walk/run while the shield is on, so that's something to think about. But he can't use attacks while in it. (Like his buster gun).
Ignore everything else in that video btw.