Mega Man (and literally every character in Smash Bros. history) is coming back to Super Smash Bros. Ultimate for Nintendo Switch. As outlined in the Nintendo Direct, Mega Man's Final Smash is a bit different: after detonating the Black Hole Bomb, Mega Man summons Proto Man and Bass in addition to previous Mega Man incarnations. Beyond that, Mega Man looks like he plays exactly as he did in Wii U/3DS. One minor difference, though, is Leaf Shield is faster and stuns each time it hits another player.
Also mentioned in the Direct, Mega Man's stage includes every trap and contraption from both Super Smash Bros. Wii U and 3DS.
And that's about it Smash Bros.-wise! Super Smash Bros. Ultimate launches December 7th, 2018!