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The game was originally advertised to have "87 bazillion" types of guns (obviously a fictional number). The actual amount is 16,164,886. Gearbox's Randy Pitchford had previously stated the number was around 17,750,000, somewhat close to the actual gun count.
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The "My Brother Was An Italian Plumber" achievement or trophy's description is "Kill an enemy by stomping on them", which is a reference to Mario.
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In New Haven there is a reference to the 1983 film, A Christmas Story. It can be found in a secret room which can be only be accessed during "Another Piece of the Puzzle". Inside is a Christmas tree, a leg lamp (made from a real leg), and a rifle called "Rider," with a caption which reads, "Careful... you might put someone's eye out".
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Attachment When Baron Flynt is killed he will drop a unique shotgun called 'Boomstick'. Its info line states 'Beyond Groovy'. This is a reference to Bruce Campbell's character Ash in the movie Army of Darkness (1992). Ash refers to his shotgun as his Boomstick and frequently uses the expression 'groovy'.
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Attachment Borderlands originally featured a more realistic art style. Early screenshots and the game's initial reveal trailer show a lack of cartoon-esque black marks on textures.
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There is a boss monster called Rakkinishu. Its name is a reference to a carver boss from Diablo II named "Rakanishu".
Rakkinishu will always drop a shield called "Cracked Sash", which shares its name with the lowest quality belt item in Diablo II.
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Within the game's files is a video file that was likely a trailer for the game. Never shown before or after the game's release, the video features the song "Greenfields" performed by the Brothers Four, as well a few small differences from the final game such as an early model for the character Lilith, and "Fyrestone" being spelled "Firestone".
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The two enemies, Skagzilla and Mothrakk, are references to the Kaiju from the Godzilla movies, Godzilla and Mothra respectively.
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Attachment In the Secret Armory of General Knoxx DLC location, Moxxi's Red Light, there are several references to the other DLCs behind the bar. There is a brain, Hank Reiss' hat, and a Jack-o-Lantern which reference the first DLC, The Zombie Island of Dr. Ned. There is also a model Claptrap with a moustache similar to that of Dr. Ned and a Marcus bobble-head.
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"The Underdome" in Mad Moxxi's Underdome Riot DLC is an obvious reference to the movie Mad Max: Beyond Thunderdome.

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