9: Mega Man 3 - Enter Proto Man

Mega Man 3 set out to expand the cast of characters on the heroic side of things, giving Mega Man the amazing robot dog Rush to assist on his mission and even, briefly, casting the supposedly reformed Dr. Wily as one of the protagonist's support team alongside Dr. Light.  Tossed unannounced into the mix was a red Mega-like robot with a signature whistling theme tune who would drop into the game on occasion and stop everything dead until Mega Man defeated him.  His identity and motives would remain a mystery until the end of the game when he's properly revealed by Dr. Light as Proto Man, a prototype robot built before Mega Man.  Later games would better establish him as an ally, but unfortunately Mega Man 5 set him up as the new antagonist which took many years for him to live down.  While the end of the Proto Man's Fortress stages reveal that the renegade Proto Man was actually part of a new plan by Dr. Wily to frame the red robot and the real Proto Man was still an ally, players who never finished the game missed out on that crucial piece of the story.  Is that why the 1990s Mega Man cartoon show sets Proto Man up as a villain and Dr. Wily's chief lieutenant?  The character would later become playable much later in the series, firmly established as one of the heroes.  Proto Man's redemption is complete, but it all started here with a mystery. 

8: Mega Man 2 - Skull Castle Exposed

Mega Man 2 expanded the franchise's formula, challenging players with larger stages, more Robot Masters, and new assistance items needed to solve platforming puzzles.  The game continued amping up the energy from the original game throughout, but it's after players defeat the eighth Robot Master that everything swings into high gear.  The original game's fortress stages were just four stages visited one after the next, but Mega Man 2 went all out to show a brief scene of Dr. Wily escaping to his massive Skull Castle fortress.  The fortress screen also served as a map to indicate just how Mega Man would storm the castle in the next level, scaling the exterior and then invading the facility's utility systems until he reached the secret underground lab where the doctor waited with a holographic alien disguise.  Each game after this one continued to show us more and more fanciful, outlandish fortresses inhabited by both the villain-of-the-week and Dr. Wily himself, but all of that tradition began here.  This incarnation of the castle is so well remembered that is reappears in the background of Mega Man's stage in Super Smash Bros. for Wii U.  Mega Man 10 even takes the Skull Castle sequence to its ludicrous extreme by tracking the fortress from the ground all the way up into space where Dr. Wily maintained an orbiting space station.

7: Mega Man 7 - Visit The Robot Museum

By the time of the seventh primary installment of the Mega Man franchise released in 1995, the series had introduced and scraped over fifty Robot Masters.  Mega Man 7 showed us the fate of boss robots defeated by Mega Man: they don't end up in a junkyard (well, except for Junk Man), but instead are rebuilt and left deactivated in the Robot Museum, a short breather level placed in between the two groups of the game's Robot Masters.  The museum is now home to Snake Man, Blizzard Man, Pharaoh Man, Heat Man, Plant Man, Flame Man, Skull Man, and Ring Man who are all visible in whole or in part in the stage's background.  Guts Man himself is stolen by Dr. Wily at the end of the stage, and he'll later be upgraded into Guts Man G in time for the Skull Castle stages.  A medley of popular stage themes from past games in the series serves as the music for the museum, and while it was great to spend a few moments basking in the nostalgia, it would've been better to visit an entire whole stage built around this concept.

6: Mega Man V - Mega Man Killers Revisited

Speaking of nostalgia, the five Game Boy games in the series take flack for being remixed variants of their Nintendo Entertainment System counterparts, but each of the first four GB games introduced at least one new element in the form of the Mega Man Killers (aka Mega Man Hunters), specialized Robot Masters designed only for killing Mega Man.  They all failed, of course, but Enker, Quint, Punk, and Ballade were rebuilt by Dr. Wily and appeared in the Game Boy grand finale, Mega Man V, in which Mega Man must blast through a gauntlet stage built out of pieces of the Killers' previous stages and, inevitably, a boss rush of the Killers themselves.  Mega Man cannot acquire their weapons this time, but it's fun to face them one more time as the Game Boy era came to an end.  Notably, the Killers (minus Quint whose place in the storyline is confusingly sketchy at best thanks to the timey-wimey nature of time travel) would appear one more time as add-on DLC for Mega Man 10 where Mega Man can acquire their weapons for use in the main game.

5: Mega Man: Powered Up - Robot Masters Enter The Fight

The Robot Masters are iconic bosses, but aside from a non-platforming spin-off title or two, the famous robots are not playable during the main action series with one exception.  2006's Mega Man: Powered Up for the PlayStation Portable allows players to rescue the original six bosses (plus two newcomers who were retconned into the storyline) instead of destroy them.  Dr. Light will fix them up, and from then on each one is playable with unique skills and characterizations in his own campaign.  Fire Man burns for justice, Cut Man is charmingly polite, and Guts Man is chiefly concerned with getting his job done on time.  Being able to take these classic characters on adventures of their own brings a new type of replayability to the formula and it's a shame that the Powered Up series did not continue so that players could control Metal Man, Snake Man, or Dust Man.

4: Mega Man: The Wily Wars - Wily Tower Mix 'N Match

Mega Man only appeared once on the Sega Genesis, but it was an appearance to remember.  Capcom ported the first three NES titles to Sega's 16-bit machine in a Super Mario All-Stars sort of experience in 1994, but with one important addition.  After completing all three games, a new short mode, Wily Tower, unlocks in which Mega Man faces off against three new Robot Masters (dubbed the Genesis Unit team) and then against Dr. Wily himself.  What makes this mode special is that players can customize Mega Man's arsenal by choosing a combination of eight of twenty-two weapons and three of seven support items from the other three games on the cartridge.  It's the only time you'll be able to take Mega Man into battle with, say, the Metal Blade, the Super Arm, the Search Snake, Item-3, and the Magnet Beam.  With so many combinations, players can take on Wily Tower again and again and again and tweak the experience each time.  It's a shame that this gimmick never resurfaced in any other Mega Man title, but with dozens upon dozens of Robot Masters weapons in the series now compared to the early 1990s, I imagine the work needed to cram them all into a game (not to mention the QA headaches) is a bit farfetched.

3: Mega Man: The Power Fighters - Zero Revealed

The futuristic spin-off series Mega Man X often makes a big deal of how it is descended from the original Mega Man series, but the original series rarely repays the favor.  There had been rumblings for years that since Mega Man X had been built by Dr. Light, then surely the competitive Dr. Wily had been working on a similar project, so what happened to it?  Mega Man X5 and Maverick Hunter X finally makes it known that X's pal Zero is Wily's creation, while the original series only calls ahead to this information once.  Finish the arcade sequel Mega Man: The Power Fighters as Bass and you'll see Wily planning his most complex robot ever with a familiar silhouette shown on the doctor's drawing board.  Even after Light and Wily are long gone, their rivalry continues through their greatest creations.

2: Mega Man 10 - Weapons Archive Is Online

Mega Man's final PlayStation 3/Xbox 360/Wii adventure featured another nostalgic surprise in Dr. Wily's latest Skull Castle.  The Weapons Archive boss launches a series of drones that are programmed with the AI and weapons of a wide range of Robot Masters from the original 1987 NES game through 2008's Mega Man 9.  Elec Man, Wood Man, Gemini Man, Ring Man, Napalm Man, Flame Man, Slash Man, Frost Man, and Tornado Man are all back in spirit one more time with Slash and Frost depicted with classic 8-bit designs for the first time, too.  While Mega Man won't earn any new weapons from defeating them, the archive is a reminder that those who don't learn their Robot Master history are doomed to be stumped by unfamiliar weapons and movement patterns.

1: Mega Man 9 - Montage Of Failure

When the original Mega Man series returned after a long absence, it reveled in nostalgia, and while we've talked about nostalgia and warm memories on this list a few times already, this final entry has to be the best instance in the entire franchise.  After defeating Dr. Wily yet again in Mega Man 9, our hero decides to show him just where he's gone wrong all of these years and uses Rush to project images from each of Wily's primary defeats across the past nine games (including Mega Man & Bass).  Rush's projections show Wily begging in each of his past fortresses and Mega Man himself is turned to the appropriate Robot Master weapon color used to defeat the final bosses.  It's a clever callback for long-time fans who remember how it all began and even now are still waiting patiently to see Dr. Wily's next humiliating defeat.

(Images via The Mega Man Network, Mega Man Knowledge Base, Corona Jumper, The Mega Man Homepage, and The Video Game Museum)