Octo Expansion

Octo Expansion is paid downloadable content for Splatoon 2. It was released on June 14, 2018 at with the 3.1.0 update.

Story
The player takes the role of Agent 8, an Octoling with amnesia who finds themself in a strange subway station connected to a series of research facilities deep underground. As the game stars, the Octoling sees Cap'n Cuttlefish ready to attack them before stopping seeing that they don't have a weapon with them. Cap'n Cuttlefish then informs the Octoling that they and Agent 3 fought in Octo Valley before "something" attacked the three and caused the Octoling to lose all of their memories in the process. Surprised, Cap'n Cuttlefish asks if they remember anything which prompts the customization of the player's Octolings. After finding a way through the beginning, Agent 8 and Cap'n Cuttlefish come across an empty platform with a lone telephone ringing. As the Octoling answers the telephone, the telephone identifies them as Subject No. 10008; being too long, Cap'n Cuttlefish decides to give No.10008 the name, "Agent 8" for short. It tells the Octoling that it would want to go the "Promise Land" so they can be free, but in order to do so, Agent 8 must collect the 4 "Thangs" so they can have a way to the promise land. As the phone ends the call, a train pulls up towards Agent 8 and Cap'n Cuttlefish and stops for them. They then meet C.Q. Cumber who is the conductor of the train and explains the functions of the CQ-80 and the credits system.

After collecting all four "Thangs", the telephone cryptically asks whether Agent 8 is "ready to ascend to a higher plane of existence" and "willing to become something greater than yourself" before using the Thangs to seemingly open a door out of the Metro. It is soon revealed to be a trap, however, and Agent 8 and Cap'n Cuttlefish realize the Thangs were parts of a giant blender that the Telephone plans to use to render them into raw material.

Before the blender can turn on, Cap'n Cuttlefish is able to send a distress call, prompting Agent 3 to crash through the ceiling and destroy the blender. Agent 3 is knocked out, but Agent 8 is able to use Agent 3's employee-model CQ-80 to activate an elevator to the surface after a lengthy escape, defeating a partially sanitized Agent 3 in the process. Once on the surface, Pearl and Marina prepare to airlift the Cap'n and Agent 8 to safety, but the above-ground section of the facility proceeds to rise from the ground, now revealed to be part of a human statue. The telephone introduces itself as Commander Tartar, an AI created 12,000 years ago to pass on human knowledge to any species worthy enough. The Commander has judged both Inklings and Octarians as unworthy of receiving its knowledge, and begins activating a weapon to destroy and recreate life on Earth, fueled by the raw material of the failed subjects that it seeks to use to create "perfect" life. Marina, Pearl and Agent 8 hurriedly put a stop to the statue, using Marina's prototype "hyper bombs" and a Killer Wail powered by Pearl's loud voice. With the day saved and Commander Tartar destroyed, Pearl and Marina return everyone home, dropping off Agent 8 in Inkopolis Plaza.

When Agent 8 returns to the Deepsea Metro, C.Q. Cumber tells them that they can now transfer credits into items as well as find Mem Medallions in different Stations that can be used to exchange items in the Vending Machine. Cap'n Cuttlefish informs Agent 8 that Agent 3 went out on patrol and he wished to check on the denizens of the deep for a while longer.

After Agent 8 completes all the tests, a locker in the Central Station will open and Agent 8 will have a battle with their "Inner Agent 3" with both of them having the classic colors of blue and orange respectively. Defeating them will reward the player with the Golden Toothpick.

Gameplay
Octo Expansion adds a new single-player campaign consisting of 80 levels. Off the Hook will support Agent 8 from above ground, and their help can be used to skip missions that are too difficult.

The first station has the Telephone, where Agent 8 learns the details on how to escape the Deepsea Metro. The Telephone also provides Agent 8 with the CQ-80 device (a flat controller shaped like a submarine), used to navigate the underground; and a CQ Card, which is used to store CQ Points.

Entering each mission costs a set amount of points, for either 1, 3 or 5 lives. The player can then choose between multiple challenges, each with a different weapon set. Depending on the weapon set chosen, a different amount of points is awarded (harder sets provide bigger rewards).

If the player loses all of their lives, they may continue from the last checkpoint with all lives returned by paying more points, return to the station for free (but still having to pay to reenter the level), abandon the level and return to the subway, or ask for help from Off the Hook to skip the level. Off the Hook can only help you skip a level if Agent 8 fails the levels at least twice. If the player fails to complete the test's conditions to pass, an inflatable balloon of ink attached to Agent 8's ink tank will explode and splat them in the process.

The normal Octarians from Octo Canyon are replaced with Sanitized Octarians, which are a distinctive shade of sickly green.

Enemy Octolings will be able to use more main weapons and special weapons, only seen in online multiplayer modes until now. For example, in the first mission (also seen in the trailer), an enemy Octoling is shown chasing Agent 8 using an. A select amount of levels will also be special only, meaning Agent 8's special bar will never go down.

Some Tests have Agent 8 go against a team of four Sanitized Octolings in a style of ranked modes. The time limit will always be five minutes and Agent 8 has unlimited lives until the time limit ends.

After completing the campaign, players will be able to play as a male or female Octoling in multiplayer gameplay and customize them just like Inklings. Gear and weapons will be shared between the characters in the same account.

A short gameplay video of one of the missions was published on April 30, 2018. It shows Agent 8 on a mission requiring her to defeat all enemies within 2 minutes. The enemies are Sanitized Octotroopers, Octosnipers and Octocommanders situated, along with Balloon Fish on floating platforms, which Agent 8 can make spin by shooting her at Ink Switches. This video also marks the first appearance of canisters similar to the special weapon canisters from Octo Canyon, as well as metallic briefcases. Both are marked with the same logo as the CQ-80 and the CQ Card, unlike the Octo Canyon canisters that show the Ammo Knights logo. The objective of the missions were revealed in a short gameplay video of Stamped-Up Station. It is a set of three floating pieces of a goal that must be covered in ink to be activated and be touched in order for the level to be completed which the level will say "TEST PASSED!" similar to the function of the Zapfishes. There are also smaller posts that emit red beacons that function the same to Mini Zapfish.

After 3 of the Thangs are found, Cap'n Cuttlefish will decide to make a "missing" poster for Agent 3, he will then ask Agent 8 what they look like which determines Agent 3's gender, skin color, and eye color.

When Agent 8 returns to the Deepsea Metro, they will now be able to use the Vending Machine in Central Station to exchange 15000 Credits for an item and go around other stations to claim Mem Medallions to be exchanged for the Vending Machine. The Vending Machine has more variety than the Ammo Knights Enhancifier, having the chance of getting more than one drink ticket, upgraded food tickets, Cash, Ability Chunks, Credits. The items range from getting every type of drink ticket to even getting tens of thousands of Cash.

Characters

 * Cap'n Cuttlefish
 * Pearl
 * Marina
 * Agent 3
 * Agent 8
 * C.Q. Cumber
 * Telephone
 * Iso Padre
 * Dedf1sh
 * Denizens of the deep

Gear
Purchasing the Octo Expansion unlocks the and the. As soon as the player enters the game and finish the Inkopolis Square News, a box containing both pieces of gear will be in the center of the Square.

14 gear items are obtainable through Octo Expansion. All players will see the items in-game, but only players who purchase the Octo Expansion will be able to obtain the items for themselves.

Music
The full version of the Octo Expansion trailer song, called "Nasty Majesty" was performed during Off the Hook's live concert at NicoNico Choukaigi 2018. On 21st May 2018, a new character was revealed. Her name is Dedf1sh and she is a Sanitized Octoling DJ. According to Nintendo, Dedf1sh was an DJ with a promising future in the music world. During her search for inspiration, she came across a deep-sea testing facility and became disinfected. Despite this, she kept up her career as a DJ, and her music will be heard all through the facility.

Stations
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Trivia

 * The expansion costs $19.99 in the US, €19.99 in the EU, £17.99 in the UK and ¥1800 in Japan. It is the first paid downloadable content announced for any game in the Splatoon series.
 * and were available early by pre-purchasing Octo Expansion. This is a throwback to the initial Splatoon Global Testfire, where players who pre-purchased  during the event were given  and  a special squid-themed layered shirt.