Title says it all. MegaMan and friends made a very small appearance in the little known GameBoy Advance game, Robopon 2: Ring/Cross Version back in 2001.
Pictured to the right is a character named 'Soul' who bears a striking resemblance to the Blue Bomber himself. Apparently, Soul's description reads: "The spirit of justice. Fight on for ever-lasting peace!" Gosh, that sounds awfully familiar.
Other characters in the game also resemble Bass, Rush, Treble and ProtoMan (whom is aptly named "Protopon").
Thanks for the tip Ji!