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From June 1st until September 8th, 2015, Canadian Yogurty's and Yogen Fruz stores offered Splatoon-themed flavors and toppings to promote the game. The two flavors available were Squidsicle - a dairy-free mango popsicle sorbet - and Inkberry, a probiotic low-fat strawberry frozen yogurt. Mango or strawberry popping bubbles were also available as toppings.

On June 15th, several select Yogurty's locations also offered customers the chance to play Splatoon while at the store.
Contributed by MeleeWaluigi
If you look inside of the entrance to the Battle Dojo while standing outside, a few Wii U controllers can be seen hanging on the wall. The controllers are a Wii U gamepad, three white Wii U pro controllers, and a black Wii U pro controller.
Contributed by MeleeWaluigi
Sunken Scroll #17 states that the Squid Sisters, Callie and Marie, are actually cousins, not sisters.
Contributed by MeleeWaluigi
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Sunken Scroll #26 contains an image of a fossilized human surrounded by a Wii U GamePad, a box with the Wii U logo, a disc, and a Wii Remote strapped to a Wii U Pro Controller. It's text says "A 12,000-year-old fossil of a creature with an odd internal skeleton. Its small skull indicates the creature was likely primitive with little intelligence. This specimen appears to have been fossilized in the middle of some kind of ritual."
Contributed by MeleeWaluigi
When Callie and Marie announce the map Moray Towers, Callie says "Rollers are super effective here!" and Callie says "Chargers are the very best, like no gun ever was!". Both quotes are references to Pokemon.
Contributed by MeleeWaluigi
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The Salt Spray Rig map was redesigned between it's reveal at Nintendo's Digital Event at E3 2014 and the game's retail release. The spawn location is lowered, and the area at the far top of the map is a lot bigger than in the final game. A number of other minor changes were also made.
Contributed by PoisonTardis
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According to Seita Inoue, during the development of Splatoon the characters started off as rabbits before becoming inklings.

"Well, a lot of it was because of design factors. Rabbits are white to begin with, so it would be easy to tell if they were inked. They've got long ears that would move when they did, so you could see them moving and when viewed from above, it would be easy to tell which direction they were facing by the direction of the ears."
Contributed by CLXcool
Despite not being able to be seen during normal gameplay, the back of the amiibo box in Inkopolis is fully detailed just like a real amiibo box. Not only this, but the text written on the box is written in the same language as that used by the squids. The only way to see this is to glitch out of the Plaza.
Contributed by alienator2013
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The Octobrush is known in Japan as the Hokusai, referencing artist Katsushika Hokusai. The design is also based on traditional Japanese brushes. Interestingly, one of Hokusai's paintings was "The Dream of the Fisherman's Wife", depicting a woman having sexual intercourse with two octopuses, tying into the English name.
Contributed by Frank Jaeger
Sunken Scroll #23 contains a music sheet that, when played, is revealed to be a rendition of the squid sisters song that plays during the 2nd phase of the final boss.
Contributed by alienator2013
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NSFW - This trivia is considered "Not Safe for Work" - Click to Reveal
Prior to the game's release, Nintendo released a demo version of the title called "Splatoon: Global Testfire". The title screen for this release featured text in the bottom right corner that was written in the language used by the characters in-game. However, the text looks very similar to a racial slur in the English language. This screen was changed in the final release to show in-game locations instead. It is not known whether this change was always intended or whether it was made to remove the offending text.
Contributed by Dazz
In May of 2015, several days before the game's release, a truck filled with copies of the game and amiibos was hijacked and stolen on its way to the UK retailer warehouse GAME.
Contributed by Boyobmas
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To promote the game, Nintendo had set-up on Santa Monica Pier an obstacle course inspired by the game where participants tried to complete it whilst getting covered in ink. A number of celebrities were also there attending the event including actor James Marsden, singer and model Alli Simpson, and actress Willow Shields.
Contributed by KnowledgeBase
According to Shigeru Miyamoto, Splatoon was almost made into a Mario game. Making it into a part of the Mario franchise would have assured sales, but it was eventually decided to keep the game as an independent and new IP.
Contributed by Mass Distraction
The ink on the floor has varying levels of depth depending on how much ink has been layered on that area.
Contributed by Dazz
The audio department created a number of the ink sound effects by taking some slime and pounding at it.
Contributed by Dazz
The music used in the game's trailer includes a number of the staff who worked on the game shouting "Splatoon".
Contributed by CamX60
The reasoning for making the game's characters into squids was because of their ability to shoot ink. Rather than being octopuses, the development team chose squids because of their arrow-like shape, allowing the player to see which direction the players on the map are facing.
Contributed by Dazz
The environment was made realistic because spreading ink all over the place reminded the development team of vandalism.
Contributed by CamX60
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There are a number of parodies of real life company logos throughout the game, including ESPN, X Games, and Gatorade G2.
Contributed by CamX60
The team that designed Splatoon is actually taken from the core Animal Crossing team. Around ten of the younger staff within the Animal Crossing team were put together to begin working on Splatoon. They were also joined by the director of the Star Fox 64 3D remake, and one of the directors who worked on Nintendo Land.
Contributed by DidYouKnowGaming
The game was developed by Miyamoto's Junior Team to be Nintendo's take on Third-Person Shooters.
Contributed by CuriousUserX90