- When the game was originally announced, it was planned to consist solely of boss battles; after its E3 reveal, Studio MDHR opted to expand the gameplay to have regular Run-and-Gun levels as well.
- Captain Brineybeard was originally named Captain Silver in a 2013 trailer.
- The E3 trailers in 2015 and 2017 showed that the game originally had black and white cutscenes, reminiscent of silent films, rather than the storybook visuals shown in the final game. They also suggest that Cuphead may have been more of a Jerkass during development, as in the E3 2015 trailer, Cuphead is shown smugly smiling over the battered body of Werner Werman as he demands his soul contract.
- Early previews for the game had different Heads Up Displays: originally, it◊ resembles Metal Slug, with a visible timer at the top of the screen. Later previews had the health meters and super meters designed like a face (with hearts being the eyes and nose and the super being the mouth), which would go into a frowny face the more damage you took. Eventually it was settled to use small and simple HUD at the bottom of the screen. Those was likely changed (and finalized to the current form) because of the additional hearts you could gain and to free up more space for the visuals.
- The 2014 build saw bosses that didn't make it into the main game, including a bat creature (likely an early version of the Devil) and a spider one. Likewise, enemy placement was different for a few of them (Cagney was on the left rather than on the right in the main game).
- An entire level, The Airship, was cut out of the game. Early demo footage shows a jellyfish-like boss with a pink orb on its head, likely to teach the player about parrying. Additionally, the level's theme can be heard on the official soundtrack. A comment by Jake Clark also implies that the level would have featured multiple minibosses (including the aforementioned jellyfish), which is supported by strings of code left in the game that refer to a stork boss, a crab boss, and a clam boss.
- There was also a Space Invaders-like minigame that was cut from the final game. Its two songs, Coin-Op Bop and High Score, were also included on the soundtrack.
- A debug menu left in the final game reveals a lot of unused content. For example, there were a few bosses cut from the King's Court: a "card" boss that's a Match-Three Game, The Light, a boss that involves dodging rotating lasers, and (by far the most complete, as well as farther along than the others) Pachi-Pachi, whose battle involves dodging falling pachinko balls and jets of flame.
- Concept art for Cala Maria shows she went through a number of alternate designs (including versions of her with hair, fin-like ears and/or a crown, and with a Breast Plate made from a clam shell rather than a Seashell Bra) and alternate attacks (including having her wield a cutlass or an anchor).
- According to the game's composer, Kris Maddigan, there was originally going to be a water-themed world. Going off of Super Mario Bros., he created a waltz tune for its music, but the world was cut, so its music became the Elder Kettle's theme. This would also explain why Inkwell Isle Three has two more bosses than the preceding worlds; the water-themed bosses, Captain Brineybeard and Cala Maria, were likely moved here after their world was cut.
- A cut boss concept that didn't make it into the game at all was a piano roll boss, where you had to dodge the sheet music in order to win. The actual music would match up to the sheet music that was playing. It was cut due to being too complicated and inflexible to implement: there'd have to be a different track for each difficulty level, and once the music was locked in, it'd be difficult to change its patterns (Cuphead uses streamed music rather than MIDI).
- Unused sprites suggest a vast multitude of ideas:
- 1. More items would be parryable (Wally's feathers and Werner's cherry bombs), Sally's husband would be fought alongside her in her third phase (as of the Nintendo Switch update he will appear if you crush him during the first round), there would be a radish mook (supposedly in Botanic Panic, and he shows up there in the new update), and Ribby and Croaks' final phase would have had a fourth attack. (More sprites of Sally's husband here.)
- 2. Sally would be able to levitate using her umbrella, the giant in Rugged Ridge would be able to throw boulders at you from the background, Cala Maria would have a third, blue held fish, Djimmi's final-phase rings would be parryable and his puppet would have a golden "invulnerable" form, Rumor Honeybottoms would have had a third magic projectile (in the form of a cube), The Devil's final phase would be fought atop his hands instead of on platforms, Cagney would have a blue alternate to his orange floating flower, and Wally would have had another, more colorful type of bullet.
- 3. A concept for a fourth "beet" boss of the Root Pack, unofficially named Betty Beet, and an alternate introductory animation for Ollie Bulb (where he is noticeably happier). (As a bonus, the radish's three animations are all assembled here.) As of the Nintendo Switch update, the alternate animation for Ollie is used; if you refrain from attacking, he'll exit the scene with the happy animation, and the aforementioned radish mook pops out during Chauncey Chantenay's phase.
- Early builds reveal that a lot more Run 'n' Gun stages were planned for each world (at least four each). The final release reduces the number to two; however, unlike the early betas, each one has a unique themenote .
- The original title screen theme is much different from the one heard in the release. It implies a slightly different plot, and doesn't reference Mugman at all. However, the ending "Cupheaaaaad!" is used when you successfully complete a level for the first time.Cuphead, who gambled away his last dime,Entered a tournament to buy him time.If he can't win his head will be shorn,And this was how the adventure was born!
- The same user who uploaded the unused sprites above, Nervatel, has also re-implemented and recorded several unused boss behaviors.
What Could Have Been / Cuphead