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Pikmin - Did You Know Gaming? Feat. JonTron
 
In the Japanese release of the game, the silencer item is worth 666 pokos. In all other releases, it is worth 670 pokos. Since the number 666 is associated with Satan in Christianity, it was likely changed to remove this connection in the West.
Pikmin 2's soundtrack contains many variations of the same songs, switching between variations based on what is currently happening, such as Pikmin carrying an item, enemies being nearby, or if sundown is occurring. Most of these variations add or remove instrumentation compared to the normal track, but if the player is controlling Louie or Spoiler:The President, the beat of the music is also given additional syncopation.
Contributed by Kitsune Hawk
By looking at the Implement of Toil treasure, the brand name is "Nintendo 64", after the console of the same name.
Contributed by Kitsune Hawk
The Decorative Goo and Master's Instrument treasures have the brand name of "Mario Paints", a reference to Mario Paint on the SNES.
Contributed by Kitsune Hawk
Pressing certain buttons on the title screen leads to a number of easter eggs, including spawning a Red Bulborb or Iridescent Flint Beetle, manually controlling the spawned enemies, and rearranging the Pikmin to spell out "Nintendo".
Contributed by Kitsune Hawk
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The logo on the Flame of Tomorrow treasure features Bowser, from the Super Mario franchise, but only in the US and European versions. In the Japanese version, the brand is instead listed as "Sun Breath", and the Bowser illustration is removed.
Contributed by Kitsune Hawk
The Cosmic Archive treasure is a Famicom Disk System disk card for Nazo no Murasame-jo (later localized as "The Mysterious Murasame Castle").
Contributed by Kitsune Hawk
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In the games files, there are unused placeholder graphics from the game Mappy. Interestingly, the game was made by Namco Bandai, who also worked with Nintendo on other games, including Star Fox: Assault, and Mario Kart Arcade GP.
Contributed by namcokid47
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Many of the game's treasures were changed when the game was localized in different regions. Many of the treasures in the original Japanese game were based on Japan-only brands and cultural references. These were changed to more appropriate brands and references in each region. This is the reason why Disk Mystery-based treasures are Japan-only, as well as the Survival Series being US-only.
Contributed by Ophl
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Unused Data in the game includes a 7th Pikmin type (the 6th being Bulbmin). Hacking the game and giving the player this type reveals they are actually Pik-Pik Carrots. They don't have much animation, and they float a bit above ground. Their stems always have a leaf on top, even if a bud, flower or spicy glow overlaps it. It also glows green when idle, like Bulbmin. They act, react and sound like any other non-Bulbmin Pikmin, and have no special attributes or defences. Finally, on the HUD, their "standby Pikmin" icon doesn't exist, and they get skipped over when calculating the closest Pikmin.
Contributed by Carlos
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Graphics for a game over screen exists in the game's data. Most of the graphics are the same as in other screens, but two of the textures are the words "GAME OVER" (one of them is likely an alpha channel). This texture is present in all versions of the game, and in all regional folders in the data.
Contributed by GamerBen144
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Gamecube discs of Luigi's Mansion, Super Mario Sunshine, The Legend of Zelda: Wind Waker & the original Pikmin were originally going to be unique treasures to collect. There textures can still be found in the game's files.
Contributed by Boyobmas
About 30% of the game's floor layout files are unused.
Contributed by Carlos
There is early English script for "Louie's Notes" that usually cant be viewed outside of hacking/cheating. Shockingly, all of Louie's Notes were changed during Development. There are also 6 missing entries. Suggesting they didn't exist early in Development They are:
Spoiler: "Hairy Bulborb"
"Decorated Cannon Beetle"
"Volatile Dweevil"
"Toady Bloyster"
"Segmented Crawbster"

and finally, the Spoiler: "Waterwraith".
Contributed by Carlos
Several pieces of information in the game hint that Louie was actually controlling the game's final boss, the Spoiler:Titan Dweevil.
Contributed by Kodyurem
Because Olimar is carrying a bottle cap in the game's intro, it would mean he has the strength of at least four Pikmin.
Contributed by Kodyurem
The game's files list the captain's folders as "orima" (Olimar), "orima3" (Louie), and "syatyou" (The President). The captain "orima2" was removed and was speculated to be Olimar's son.
Contributed by Kodyurem
By going to any dungeon you have not completed and getting every treasure there, you will be brought to a special results screen. By waiting at this screen for about four minutes, Totaka's song will start playing.
Contributed by gamemaster1991
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The Awakening Wood has the exact same layout as The Forest of Hope from the first game. In the entry for the Geographic Projection (which is found in the Awakening Wood), Olimar says that he "explored this forest the last time he was here, but it has undergone some dramatic changes" and that he has "given this forest a new name." Both of these hints that both areas are one in the same.
Contributed by gamemaster1991
If you put 20 of each color Pikmin into your party they will start singing (or humming) a secret song. This song was actually a promotional song for Pikmin 1 in Japan and is called 'Ai no Uta'.
Contributed by Boyobmas
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The four levels seem to be based off the four seasons. The first level(Valley of Repose) is winter, the second level(Awakening Wood) is spring, the third level(Perplexing Pool) is summer, and the last level(Wistful Wild) is fall.
Contributed by oozy the wolf