Last week, we were able to catch a glimpse via Miiverse screenshot of what Mega Man will look like in Nintendo's new Super Mario Maker for Wii U when you acquire the amiibo mushroom that powers Mario up into the Blue Bomber. Since then, more members of the press (not including myself yet, unfortunately) have begun experimenting, yielding some videos of the characters in action.
Unfortunately, Nintendo of America filed a copyright claim against the video Vhyper1985 sent to me, so I've had to look around for another. There isn't much there, mostly "sampler" videos like the following which serve to give you a brief look at the visuals and sound effect you hear when you transform before moving on to the next one.
Fortunately, Mega Man just so happens to be the very first in line:
Watch further to see more of the amiibo transformations, of skip to 4:55 to see Mega Man in a little more action.