Mega Man 2 takes place after the original Mega Man, which is set in an unspecified year during the 21st century (the year 200X). Dr. Wily, the series' main antagonist, builds a new fortress and army of robotic henchmen, led by eight new Robot Masters of his design. Mega Man is sent by his creator, Dr. Light, to defeat Dr. Wily and his Robot Masters. Mega Man crushes the eight new Robot Masters and then challenges Wily himself. In the final fight, Mega Man defeats Dr. Wily's holographic projection device. After the scientist begs for mercy, Mega Man spares Wily and returns home.

Mega Man 2 was developed and published by Capcom. In retrospect, series producer Keiji Inafune described the game's development as a "rogue effort". The first Mega Man game—released in 1987—was not successful enough to justify the immediate development of a sequel. Capcom allowed the development team to create a sequel on the condition that they work concurrently on other projects as well. The staff spent their own time on the project to improve upon the original by adding more levels and weapons, as well as improving the graphics. The project supervisor of the first Mega Man invited Inafune to the sequel's development crew; Inafune was working on a separate game at the time. In the previous title, Inafune worked as an artist and character designer, but became more involved in the production process of the sequel. "Working on [Mega Man 2] marked my second year at this, and I even got to mentor a 'new kid', which opened up a whole new world of stress for me," Inafune recounted. The development time for the game was only three to four months.

Due to the limited amount of cartridge space available for the first game, content was omitted from the final product. The unused elements were later transferred to Mega Man 2. The team was limited by the graphical capabilities of the console, and designed characters as pixel art to maintain consistency between the designs and final product; some design elements, however, were lost in the transition. The gameplay system from the original game was kept for Mega Man 2, but the team included more traps for the player to navigate. The game's three support items were added to aid the player because of complaints from consumers and Capcom's marketing department regarding the original game's high difficulty. Inafune's supervisor was "especially unsure" about the usefulness of the Energy Tanks. The developers allowed input from the public by including boss designs created by fans. Capcom received 8,370 boss submissions for the game, although even the designs for the final eight Robot Masters were "tweaked". Inafune intended his artwork for Mega Man 2 to be more "anime-ish" than in the first game. A second difficulty setting was added for the North American release. The original version was labeled "difficult", and a "normal" setting was created that made the enemies weaker.

The soundtrack for Mega Man 2 was composed mainly by Takashi Tateishi, credited as Ogeretsu Kun (a nickname implying rudeness, geretsu (下劣) meaning rudeness or depraved in Japanese). Ippo Yamada, sound designer for Mega Man 7, explained that even in 1995 "Capcom... was just beginning to transition from crediting staff members by aliases to their full names."Manami Matsumae, who had composed the music for the first Mega Man, also made some contributions to the soundtrack of this game, in particular the title screen overture (which she had previously written for the first game's ending) and the music for Air Man's level. As with the previous game, the sound programming was handled by Yoshihiro Sakaguchi.

Though the first Mega Man game had relatively low sales, Mega Man 2 was a huge success. Since its 1988 release, Mega Man 2 has sold over 1.5 million copies worldwide. The game is the highest selling in the Mega Man series and is Capcom's 30th highest selling title.Mega Man 2 was well received by critics. Electronic Gaming Monthly's four reviewers—Steve Harris, Ed Semrad, Donn Nauert, and Jim Allee—rated the game favorably. They stated that it was better than the first Mega Man, citing the improved audio-visuals, new power-ups, and password system. Nauert and Allee, however, expressed disappointment that the game was less difficult than the first game. Nadia Oxford of 1UP.com complimented its aesthetics and gameplay. She further stated that Mega Man 2 improved the gameplay of its predecessor by removing excessively difficult elements.Mean Machines' two reviewers, Julian Rignall and Matt Regan, praised several aspects of the game. Rignall lauded the gameplay, citing its addictiveness and the puzzles. Regan praised the difficulty and called the gameplay balanced. Both reviewers complimented the graphics, calling them detailed and stunning, and described it as a great platform game.Retro Gamer editor Richard Burton described it as a "must-have" title for the system, comments echoed by two of Electronic Gaming Monthly's reviewers. Zach Miller writing for Game Informer attributed the success of the game to the players' option to defeat the stages in the order of their choosing. He praised the simple control scheme and variety of weapons and items.

The game's soundtrack has been well received by critics. Joey Becht of IGN listed three stage themes from Mega Man 2 along with the main title song among the best in the series. In 2008, Game Informer listed Mega Man 2's introduction sequence as the fifth-best video game opening, citing the build up of excitement that the music and appearance of the character instills. The "Doctor Wily Stage Theme" was ranked second in ScrewAttack's "Top 10 Video Game Themes Ever" video.Nintendo Power' editorial staff praised the music in 2008, stating it is among the best on the platform. In 2009, Gamasutra's Brandon Sheffield describe the music as easily recognizable, and lamented that contemporary video game music lacked that trait.

Mega Man 2 is a favorite among Mega Man fans, with many calling it the best in the series. Critics have also referred to the game as the series' best title. Oxford considered it one of the most memorable titles in the series, and Burton called the game the best in the series.IGN's Levi Buchanan listed three of the game's bosses among the "Top 10 Mega Man Robot Masters". Several publications consider the game a critical success and have listed it high on "top game" lists. At the end of 1989, it was the top ranked game on Nintendo Power's Top 30 list. In August 2008, Nintendo Power listed Mega Man 2 as the third best Nintendo Entertainment System video game. The editorial staff praised the polished improvements over the previous game.GameSpot named Mega Man 2 as one of "The Greatest Games of All Time". It ranked number 33 in Nintendo Power's "Top 200 Nintendo Games Ever" list and number 60 in Official Nintendo Magazine's "100 Best Nintendo Games" list. Miller considered it one of the greatest games of all time. In 2007, IGN's three editorial offices—United States, United Kingdom, and Australia—compiled a list of top 100 games. They listed Mega Man 2 as number 67, citing the action and strategic elements along with the impact it had on the series.Mega Man 2 was placed 4th on IGN's list of the Top 100 NES Games.

Keiji Inafune claims the success of Mega Man 2 is what made the Mega Man series a hit that continues to spawn sequels.1UP.com's Kat Bailey commented that the game helped establish the series as a prominent and commercially successful video game franchise. IGN cited Mega Man 2 as a title that helped define the action-platforming genre.Retro Gamer credited it with helping the series obtain the global presence that allowed spin-offs and more sequels to be created. Many of the conventions of the original Mega Man series were defined by the first title, but Mega Man 2 added conventions that were retained. The traditional number of Robot Masters for the series is eight as used in Mega Man 2, rather than the six used in the original. It was the first in the series to include an opening cinematic.Mega Man 2 also introduced the Energy Tank item, special movement items, teleporter room, and password system, which became staples in future titles. The Energy Tank became the series' iconic health refill item and later served as inspiration for a promotional "Rockman E-Can" drink. In developing Mega Man 9, producer Inafune and Hironobu Takeshita looked to the first two games in the series for inspiration, with Mega Man 2 serving as a standard to surpass in order to meet fans' expectations.Mega Man Universe was to feature a remake of Mega Man 2's story campaign, as well as feature customizable characters and levels. However, Capcom has officially announced the game's cancellation due to "various circumstances."

Rereleases and novelization

Tiger Electronics produced a handheld electronic version with abridged gameplay. In 1999, Mega Man 2 was rereleased for the Sony PlayStation as the second of six Rockman Complete Works discs, though only in Japan and under the original title Rockman 2. It is largely identical to the original NES release, but had a number of bonuses, such as a "navi mode" for beginners that presents the player with a slightly re-made version of the game, detailed encyclopedic content, image galleries, and remixed music.Mega Man 2 was included with nine other games in the series in Mega Man Anniversary Collection for the Sony PlayStation 2, Nintendo GameCube, and Microsoft's Xbox, released between 2004 and 2005. The game's emulation is identical to the rerelease contained in Rockman Complete Works. Also in 2005, Mega Man 2 was released alongside other Capcom games as part of a "Plug It In & Play TV Games" peripheral by Jakks Pacific.Mega Man 2 made its way to mobile phones in 2007. The game was added as a part of the Wii Virtual Console service in PAL regions on December 14, 2007. In celebration of the ninth title's release in September 2008, Capcom Japan released the game in Japan on August 26, 2008 and a North American release on September 15, 2008. In March 2009, Capcom released the game for iOS, while in September of the same year the Complete Works version of Mega Man 2 was released on the Japanese PlayStation Store, making it available for download on the PlayStation 3 and PlayStation Portable. Inafune expressed a desire to remake Mega Man 2, similar to Mega Man Powered Up, but stated that such a project was dependent on the commercial success of the latter. A tech demo for the Nintendo 3DS called Classic Games was shown at E3 2010, displaying more than a dozen classic games, including Mega Man 2, using 3D effects. Reggie Fils-Aime announced that the titles were slated for release on the 3DS and would possibly use the 3DS' features, such as 3D effects, analog control, or camera support. The game was released on the 3DS via the Virtual Console in Japan on August 8, 2012 and was released in Europe and North America on February 7, 2013.

Mega Man 2 was novelized in the Worlds of Power series published by Scholastic in 1990. The novel mostly follows the game, even offering game hints at the end of some chapters. Besides the added dialogue, the one major variation in the novel is that Dr. Light fears Mega Man's chances against Dr. Wily's more powerful new robots and while attempting to duplicate him, accidentally turns him into a human being, a difficulty Mega Man must endure throughout the story. The book's cover also lacks the gun depicted on the North American boxart of the game, due to a "no weapons" policy that Worlds of Power writers had to abide by.

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