- Mega Man was originally a licensed game based on Astro Boy. The license was pulled during the game's development, leading to a whole new franchise.
- An interview with planner Akira Kitamura reveals that Mega Man 2 was supposed to have an Easter Egg in Wood Man's stage, where shooting off an Atomic Fire blast would start a forest fire and cause all of the Battons nesting in the trees to fly away. This was scrapped before release, but the animated palette that was supposed to be used for the fire animation is still in the ROM. The idea may have inspired the ability to burn away foliage in Sting Chameleon's stage with Fire Wave in Mega Man X1.
- The classic yet infamously cheesy and Off-Model Ruby-Spears cartoon was originally planned to actually be design-accurate to the game artwork, complete with all of the cast members being sized to their almost chibi-esque selves, as revealed in the uncovered sales pitch VHS. Unfortunately, or perhaps fortunately depending on one's view point of how the series held up at the time, the art style did not gel well with focus test groups, causing Ruby-Spears to rework everything to better fit the more marketable styles of children's action cartoons in the early-to-mid 90's. Parts of the sales pitch animation are still used in the final opening, and one can attribute the poor test reception to anime simply not having caught on quite yet in the west at the time. Incidentally, the exact animation style would be reused for Mega Man: Upon a Star, done by the same studio that both animated for the cartoon and the sales pitch as it was originally intended to be a special episode for the series.
- The Maverick Hunter X series was supposed to be Inafune's reimagining of the Mega Man X series, with updated graphics, voice-acting, animated cutscenes, and better focus on plot and characterization. Unfortunately, low sales of the first MHX game has scrapped the series. When the Mega Man X Collection was first announced, there were plans to add enhancements and redub the later games. However, the idea was scrapped when the developers decided to simply put those features into the Maverick Hunter X remakes. Thus players received a collection of straight ports retaining the same faults as the originals, and the proposed series was, as mentioned above, cancelled.
- Mega Man X falls into this too. Keiji Inafune, the producer of the majority of the Mega Man series, originally created Zero as the protagonist of the game; however, he eventually decided that Zero looked too different from the original Mega Man to be easily sympathized with by long-time Mega Man fans, so he turned Zero into X's somewhat cooler friend and mentor, delegating the authority of creating the true main character to someone else.
- Mega Man X2 was supposed to have a fourth, female member of the X-Hunters, but she, alongside a second form for one of the others, was scrapped due to technical limitations. They were also supposed to be called the "Four Guardians" before the cut was made; the name was reused in the Mega Man Zero series.
- After Mega Man X5, Inafune intended the series to end so he could begin with the Mega Man Zero series, but Capcom executives released a Mega Man X6, without his input, just so they could continue to cash in. And that is the reason you don't mention Axl in hardcore MMX fan forums. Also, when the Zero series was being made, Inafune had to adjust his desired plot due to the continuing X series and Executive Meddling. X was supposed to be the villain of the first game, changed to an imperfect clone. It was also going to delve into Zero's origin, but that was scrapped.
- At one point, these guys, Baroque and Crash, were meant to be Mega Man and Rush's rival, but they were heavily reworked into, you guessed it: Bass and Treble.
- And then, there's Bond Man. Apparently the original Mega Man was intended to have 8 Robot Masters instead of 6 - 7 had been designed when technical limitations pushed the number down to 6. The cut Master was the glue-based Bond Man. Oddly, despite Mega Man Powered Up being a remake of the first game with two new Robot Masters, Bond Man does not appear, because the developers wanted him to remain an enigmatic "Lost" character.
- Because the developers took fan submissions for Robot Masters from Mega Man 2 to Mega Man 8, roughly 750,000 bosses were at one point or another under consideration for the games.
- Mega Man was originally going to have the ability to crouch in the first game. This was scrapped when it was decided that the graphical limitations of the NES made it too hard to determine whether a projectile needed to be crouched under or jumped over. The fan-made game Mega Man Rocks averts this by allowing Mega Man to crouch.
- In Mega Man 3, Rush's third ability was to have been Rush Drill rather than Rush Jet.
- Mega Man Battle Network's prototype storyline originally had a few differences from the final product:
- Lan was supposed to lead a group called Right to fight against a prototype World 3 called WWPO (it was scrapped so that Lan could go solo, although he joins a group in BN 5).
- Chaud was supposed to be rich and to treat net navis as no more than tools.
- There was supposed to be a character named Mike Kenan, who was to be a high school age kid, that was an official netbattler (these two were merged, to create Chaud's final personality).
- Mike was to pass his net navi Roll.EXE to Mayl/Maylu and then take Bass.EXE as a new navi (changed to her having Roll from the beginning, and to Bass being a solo net navi).
- Mayl/Maylu was supposed to participate in the final battle against the Lifevirus (changed, but she still appears prior to that battle, along side Chaud).
- Back when Mega Man Anniversary Collection was announced, there were going to be two versions - the console version we got and a handheld version for the Game Boy Advance that would bring back the five Game Boy Mega Man games. However, it's said that the games' original code was lost and thus the project was scrapped.
- For Mega Man 9, we could have gotten Cement Man◊, Weather Man◊, Ocean Man◊, Plasma Man◊, Diamond Man◊, Honey Woman◊, and Space Man◊. In other words, Splash Woman and Hornet Man ended up swapping genders during production.
- As shown here, there was going to be a first person shooter game based on the Mega Man X series.
- Mega Man 11 would have featured a female Robot Master (the second one after Splash Woman), but she was scrapped due to her weapon not meshing well with the game's play style.
- Mega Man Star Force 4 would feature the game going in a Darker and Edgier direction. Geo Stellar would have teamed up with a boy named Kazuma who happens to be a direct descendant of Lan Hikari. The two would become hackers and be wanted by the Satella Police. The game was in production at one point but was cancelled due to lackluster sales from both Star Force 3 and Operation Shooting Star.
What Could Have Been / Mega Man