Though ideas for a bird support utility weren't realized until the inclusion of Beat in Mega Man 5, this idea evidently traces back to the development of Mega Man 3, as shown in the Mega Man Official Complete Works art book.
The attack "Hard Knuckle" may possibly be a reference to the manga/anime "Mazinger Z (マジンガーZ)", in which the titular robot uses a very similar attack known as "Rocket Punch (ロケットパンチ)". The colors Mega Man also has while using this weapon bear a strong similarity to the colors of Mazinger Z's arms and fists.
In the Japanese version a room near the end of Wily stage 1 has a different layout. The international layout removes the platform in the middle of the screen and moves the weapon capsules to a lower platform on the far right, probably to make them easier to get to. This also forces the player to switch weapons mid-air if they don't want to refill Rush Coil or Rush Jet.
After a week of work on Top Man, his data was lost due to a computer crash. Keiji Inafune spent another three days rebuilding it from scratch, making Top Man one of his most memorable creations.
Several debugging features were left in the game, and can be accessed by holding certain buttons on a second controller. Holding right will dramatically the height of Mega Man's jumps, and also protect him from "bottomless" pits. Holding up will slow down the game's animations, and holding A as well as up will pause them completely.
The two Robot Masters on the American cover (Spark Man in the foreground, Top Man in the background) are the given the wrong colors. Spark Man is all gray when he is meant to be a mix between orange and gray, while Top Man is green when he is meant to be orange.
Keiji Inafune considers this the least polished of the Classic series, as they didn't have that long to work on the game (roughly a year), and many things kept going wrong during development. Inafune told Nintendo Power, "If we had more time to polish it, we could do a lot of things better, make it a better game, but [Capcom] said that we needed to release it."
Doc Robot's name in Japan is ãƒ‰ã‚¯ãƒãƒœãƒƒãƒˆ(Dokurobotto), a combination of two words, dokuro (skull) and robotto (robot). His name is a pun of how he looks, which is lost in translation when coming to America.