Ryu Hayabusa Trailer
The first trailer introduced Ryu Hayabusa as a playable character. This one really freaked people out.
Version 1.1 Trailer
The Version 1.1 trailer has a Mega Man 2 theme and goes over some new features that were added.
Sophia III Trailer
The second character trailer introduced Sophia III as a playable character.
Version 2.0 Trailer
Version 2.0 introduced a lot of new features, but skinning was the main one. I really like the end when Bass and Mega Man fight.
Version 3.0 Trailer
This one introduced the levels from Super Mario Bros. Special, some new skins, and easy/hard versions of levels.