"SQUARE UP", a song contributed to the Breakout Edition expansion by American electronic musician Jamie Paige, prominently references her 2022 song "(:women_wrestling:)" (itself later included in UNBEATABLE - THE JAMIE PAIGE CONTENT COMPANION, the game's first paid DLC pack). Not only do both tracks utilize fistfight imagery as a metaphor for love, but "SQUARE UP" also features multiple lyrical callbacks to its predecessor. The line "But there's a bullet kept inside my zone" references the "(:women_wrestling:)" line "I keep a bullet with your name inside my zone", and the "SQUARE UP" lines "Back to back / Beat some ass" are directly sampled from the 2022 track. The callbacks to "(:women_wrestling:)" are furthered in the music video for "SQUARE UP", two scenes of which feature illustrations of Gumi wearing the same outfit from the 2022 song's cover art. Both the illustrations and the "(:women_wrestling:)" cover art are additionally done by the same artist, Bearvamps.

These ties are further amplified in UNBEATABLE - THE JAMIE PAIGE CONTENT COMPANION, where purchasing both it and the Breakout Edition unlocks "SQUARE UP [SYNTHETIC]", a remix featuring earlier versions of Gumi and Kasane Teto's voice banks. This rendition directly samples additional lines from "(:women_wrestling:)" both after the second verse and during the outro.

The title and cover art for "ball is infinite" reference a notorious Easter egg from Sonic CD, where toggling the sound test to a specific combination produces a screen depicting multiple copies of Sonic the Hedgehog with humanlike faces and text atop translating to "Infinite fun. Sega Enterprises. –Mazin Picture". The "ball is infinite" cover art similarly depicts multiple copies of Beat mimicking Sonic's pose with Quaver's face superimposed atop hers. Also like the Sonic CD screen, the text on the "ball is infinite" cover is written in Japanese with "infinite" represented by an infinity symbol, though an English translation is provided below. A looser translation of the Sonic CD screen's text, "Fun is infinite with Sega Enterprises," forms the basis of the song title.

Within the game's data is an unused placeholder cover image for a custom song, consisting solely of a stock image of a picture frame and comedic text congratulating the player for importing their own music into the game. The image was likely used to test the PC version's custom beatmap feature, which, incidentally, was not officially announced until nine days after the placeholder's discovery.

Within the game's data are two placeholder assets depicting copyrighted material:

• The first is a placeholder album cover depicting an edited comic by cartoonist Asher Perlman, wherein a group of bar patrons run to stop a middle-aged fan of the American jam band Phish from using a jukebox. The comic became a meme shortly after it was uploaded, replacing the Phish logo on the man's shirt with other pieces of iconography. In this case, the edit found within the game's files inserts artwork of virtual YouTuber and rapper Mori Calliope. This version of the image is not unique to the game, having originally been posted in 2022 by Twitter user TheKnownOtaku as part of a thread ridiculing the idea of friend groups intentionally listening to music they dislike together.
• The second is a doodle of the character Snoopy from the American comic strip Peanuts, used as a temporary item icon.

Within the game's data are unused sprites for a cut character named Mindy, likely a prison inmate given her apparel. A much earlier version of this character with a substantially different design was previously showcased in a 2019 build of the game; the only publicly available images of this rendition are a meme posted on D-CELL's Twitter account parodying tropes in mobile game advertisements and an emote on the game's Discord server.

Pre-release material for UNBEATABLE showed that Beat's journal originally featured additional tabs containing a map, a song list, and a to-do list, the latter of which would track main events and sidequests via a diary that Beat would update as the player progressed. By 2025, the map tab was replaced with the items tab, and come the final release, the "Songs" and "To-Do" tabs would be excised altogether. Despite this, assets pertaining to the "To-Do" tab are still present in the game's files. The pages seen in the Day of the Devs 2021 trailer are almost entirely intact in the journal's object tree, albeit with slight modifications, while text for various other entries pertaining to Episode Three are present in the game's dialogue system.

Within the game is unused text and audio pertaining to scenes that were scrapped from Story Mode:

• A dream sequence in Episode 2 where Beat reminisces on her time working as a corn detasseler as a kid. The ending of the sequence would've revealed that one of the other child workers had a severe accident on-site, which resulted in Beat quitting the job and receiving $62 in what is implied to be class-action settlement money.
• A scene in Episode 5 which would've revealed how Spoiler:the rest of UNBEATABLE found out about Beat and Penny's infiltration of HARM's headquarters. After the band's argument with Beat, the members would've stumbled upon the remains of Penny's studio after its destruction by HARM; Clef would then intuit that Beat decided to get revenge. In the final game, Beat's band members are only shown to have known about her excursion when they stop her from killing Sforzando.
• A voice-acted version of Spoiler:Beat's reunion with her sister (revealed to be named Brianna) after returning to her own world during the ending. The conversation would've made it more explicit that Beat's leap into the game's universe occurred simultaneously with her physical body being left comatose after being run over, with Beat reawakening midway through Brianna's ruminations on the pair's falling out.

Additionally, the game's data contains additional dialogue for the scene where two cops watch a news report about Treble and Clef's arrest at the start of Episode 2. Specifically, while one cop's lines are present in the final game, the other's were disabled in an update, rendering them unused.

Within the game's data is an alternate version of the sequence in Episode 6 where Spoiler:Beat and Rest rescue Poco and Apoco from the Silence. This sequence takes place at night on a beach by the lighthouse, which is toppled over, rather than at sunset outside the intact lighthouse proper. This rendition also triggers Spoiler:the same cutscene and boss fight featured in the final game, though Poco and Apoco use their standard sprites rather than their "Nothing" ones.

The in-game version of "Bookend Song" censors Quaver's line "I'm so fucking tired" by muting the word "fucking"; the line appears uncensored in ALBUM., an official compilation of diegetic songs from the game's soundtrack. In a meme posted on Bluesky, D-CELL GAMES staff member Jeffery Chiao implied that the censorship was done in order to avoid an M rating from the ESRB.

Within the game's files is an animatic for an FMV version of the sequence preceding "Waiting" in Episode 2. In the final game, this sequence instead plays out via standard gameplay save for the shot of Clef discovering the drones pursuing the train, which is fully animated.

Unusually, this animatic was not present in the base release's data, but was added in the 1.8.0 update and features a considerably different series of events. Beat, Clef, and Treble throw themselves into the train while following Quaver, just barely escaping a police officer, rather than the four arriving at the train station from different escape routes just before the train arrives. The quartet has a more fleshed out conversation about their status post-escape before Clef shushes Quaver, hearing the buzzing of drones from outside. The sequence where Beat and Quaver recreate one of Eve's photos is also absent. Some voice-acted dialogue from this scrapped rendition is retained in the final game.

When Eli Stavridis announced in a 2022 tweet that she had joined D-CELL GAMES as an animator for the game, her post included line-art of a frame matching a scene from this storyboard, indicating that it progressed to some level of animation before being scrapped. This was later confirmed when another animator, Star Ren, posted a video to YouTube compiling their contributions to the game. This video includes work in progress snippets of the scrapped cutscene, showing fully animated and colored versions of the game's cast and incomplete backgrounds. Similarly, Clef's animations in the shot of her discovering the drones are identical to the final game.

The track "Motherbound" is a reference to the MOTHER series of video games:

• The song's title is a portmanteau of the series' Japanese name, MOTHER, and its English name, EarthBound.
• The song's flavor text, "say fuzzy pickles", is the catchphrase of the Photo-man who intermittently appears throughout the second game in the series.
• The name of the song's Star difficulty, "Boing!", quotes a verbal tic spoken by the Mr. Saturn species from the series.

The version 1.9.0 update replaces the original mix for the Breakout Edition track "Goin' Crazy" with a substantially different mix featuring added, removed, and rearranged vocal effects, samples, and lyrics. This updated mix is also the basis for the song's music video. According to D-CELL, the original mix was a rough draft not meant for public release, with the remix in version 1.9.0 reflecting the intended final product.