Mega Man (known in Japan as Rockman) is the protagonist of the Mega Man series by Capcom. He was originally a lab assistant robot, but was later turned into a fighting robot to protect the world from the evil scientist Dr. Wily and his evil Robot Masters. He has appeared in various crossover titles, including the Marvel vs. Capcom series and Super Smash Bros. for Nintendo 3DS and Wii U.
Mega Man was originally a lab assistant robot named Rock, who was built by Dr. Thomas Light with the ability to utilize different tools. After Dr. Wily steals the original six Robot Masters from Dr. Light's lab and reprograms them for world domination, Rock volunteers to be converted into a combat robot, with the intention of retrieving the stolen Robot Masters and bringing Wily to justice. Now known as Mega Man, he now possesses the Mega Buster, a cannon built into his right arm which can shoot powerful plasma blasts. The systems that governed his ability to use tools was then repurposed into the Weapon Copy System, which allows him to replicate the powers of the Robot Masters he defeats.
In M.U.G.E.N, Mega Man has been made by several creators. Many versions of the character are based on his appearance in the fighting game Marvel vs. Capcom, with JinKazama's being the one more similar to his original incarnation, while others, despite using sprites from said game, have completely new movesets and color palettes.
Though the first and not the best super fighting robot, this one has elements from Marvel vs Capcom combined with an original Level 3 hyper and a Protoman striker.
NES Mega Man is a version of Mega Man created by Hsiehtm, who is based on his appearance in the original games for the Nintendo Entertainment System (known as the Famicom in Japan). This version plays exactly like he does in his 1-6 and 9-10 games, specifically Mega Man 2.
He is able to shoot bullets from his Mega Buster, and use three special weapons from Mega Man 2: Metal Blade, Air Shooter and Time Stopper.
While not a bad or good Mega Man, this is one you should try out if you don't like his Marvel vs. Capcom moveset. He's now more like a shotoclone, of sorts.
Another MVC-Styled Mega Man, this one is generally loyal to the original game, but has new abilities such as calling his robot friends as strikers, and more cooperation with his robot dog Rush, allowing him to transform into a coil to make Mega Man jump higher, or into a jet that allows Mega Man to fly in the air.
But the main feature of this Mega Man is a special transformation, which allows Mega Man to merge with Rush and gain a completely new moveset.