On December 7, 2022, the game's official Twitter account announced the release of UKButt, an official mod which adds overall controller rumble support to Ultrakill by running buttplug.io, an open-source program that allows select video games to interface with rumble motors in Bluetooth-connected devices, and is especially designed and marketed for use with adult toys. The announcement described the mod's release as the "Sex Update," referencing a longtime meme among the game's fanbase which jokingly demanded that Hakita "add sex to Ultrakill," to the point of leaving tongue-in-cheek negative reviews on Steam.

Many of the game's equipment items, enemies, and levels are named after popular music:

• The Feedbacker is named after the 2003 album by Japanese drone metal band Boris at Last.
• Whiplash is named after the 1983 song of the same name by American thrash metal band Metallica.
• Schism is named after the 2001 song by American progressive metal band Tool.
• Streetcleaner is named after the 1989 album by English industrial metal band Godflesh.
• In "Overture: The Mouth to Hell", V1's bootup sequence dates their firmware to the year 2112, referencing the 1976 album by Canadian progressive rock band Rush.
• "1-1: Heart of the Sunrise" is named after the 1971 song by English progressive rock band Yes.
• "1-2: The Burning World" is named after the 1989 album by American experimental rock band Swans.
• "1-3: Halls of Sacred Remains" plays on the song "House of Sacred Remains" from the soundtrack to Castlevania: Lament of Innocence.
• "1-4: Clair de Lune" is named after the third movement from French impressionist composer Claude Debussy's Suite bergamasque. "4-3: Clair de Soleil" further plays on the song, replacing "lune" (moon) with "soleil" (sun).
• "2-1: Bridgeburner" is named after the 2015 song by American heavy metal band Mutoid Man.
• "2-2: Death at 20,000 Volts" is named after the Tokyo Nightclub 20000V.
• "2-3: Sheer Heart Attack" is named after the 1974 album and 1977 song by English glam rock group Queen.
• "2-4: Court of the Corpse King" is a play on the 1969 song "The Court of the Crimson King" by English progressive rock group King Crimson.
• "2-5: All-Imperfect Love Song" is named after the 2002 song by Japanese electronic musician World's End Girlfriend.
• "3-1: Belly of the Beast" is named after the 2014 song by English experimental musician Gazelle Twin.
• "3-2: In the Flesh" is named after the 1979 song by English progressive rock band Pink Floyd.
• "4-2: God Damn the Sun" is named after the 1989 Swans song.
• "4-3: A Shot in the Dark" is named after the 1986 song "Shot in the Dark" by English heavy metal musician Ozzy Osbourne.
• "5-1: In the Wake of Poseidon" is named after the 1970 King Crimson album and its title track.
• "5-2: Waves of the Starless Sea" references the 1974 King Crimson song "Starless".
• "5-3: Ship of Fools" references the 1970 song by American psychedelic rock band the Doors.
• "5-4: Leviathan" references the 2004 album by American heavy metal band Mastodon.
• "6-1: Cry for the Weeper" references the 2005 song by American drone metal band Sunn O))).
• "6-2: Aesthetics of Hate" references the 2007 song by American heavy metal band Machine Head.
• "P-1: Soul Survivor" references the 1972 song by English blues rock band the Rolling Stones.
• "P-2: Wait of the World" references the 2013 song "The Wait of the World" by American avant-garde metal band Kayo Dot.