Just my suggestion for a Mega Man B-Set.
Neutral:Buster. Can run and jump while charging. Can shoot 3 uncharged shots and 1 charged shot of any level. Uncharged shots do as much damage as a single Super-Scope shot. Second level charge should do about the damage of Tink's Bomb. Third charge should do as much damage as Samus's.(I was about to say a fully-charged shot from the Super-Scope, but that would just be broken.)
Side B:Metal Blade. Works like Ivysaur's Razor Leaf, or Link/Tink's Boomerang. He changes weapons, and in the time that you change weapons, you can edit it's trajectory. You can rapid-fire up to 2 shots from it.
[OR]
Tornado Hold. Mega Man shoots a small fan onto the ground. This fan blows people(and Mega Man) upwards. If shot offstage, it can actually save people.
Up B:Flight Adapter. Similar to Pit's up-B, if Mega Man gets hit out of it, he cannot use it until he either grabs the ledge or touches the ground. Hitting him will also knock him out of it.
[OR]
Rush Jet. On the ground, Rush appears, and Mega Man has free roam of the stage for a few seconds. Again, like Pit's Up B. Only cooler, cos' he's a robot.
Down B:Leaf Shield. A shield of Metallic leaves forms around him. He can move freely, but can do no other special moves while in the Leaf Shield. If hit, no matter how hard the hit, the Leaf Shield will protect him. If Down-B is pressed again, he will shoot it forward.
Other moves:
DSmash:Charge Kick-- A slide forward, similar to Falcon Kick. The difference is that it does not go as far, and it always goes the same distance, even if you hit someone.
Final Smash:Upgrade to X-- Mega Man jumps in the middle of the screen, lights flash, and armor pieces attach to him, making him into Mega Man X. He is stronger, and his Special moves are all much stronger. 5 uncharged Buster shots onscreen at once, and the ability to throw 2 charge shots at once by pressing b right after you fire the first. The second one can KO at really low %'s.