Return of the Mammalians

"Join Agent 3 and the New Squidbeak Splatoon in a hairy fight against the unruly Octarians. Discover the secrets of Alterna and the Fuzzy Ooze."

- official website

Return of the Mammalians is a single player game mode in Splatoon 3. It involves the player donning a Hero Suit and venturing into the Crater and Alterna (the setting of the story) to defeat the Fuzzy Octarian army.

Story
An Inkling or Octoling, accompanied by their "little buddy" Smallfry, are scrap hunters who search for junk gems by day and splat it up in Turf Wars on the side. When they go through a manhole, they meet Craig Cuttlefish on the other end at the Crater, who dubs them the new Agent 3 of the New Squidbeak Splatoon. The New Squidbeak Splatoon's mission is to stop the continued fight against the unruly Octarians, who are suspected of the recent disappearance of the Great Zapfish in Splatsville.

The areas throughout the campaign have a large amount of Fuzzy Ooze. To get through areas, Agent 3 has to take care of the Fuzzy Ooze, which Smallfry can eat as long as they have the right amount of Power Eggs. Cuttlefish also notices that the Octarians have fur grown over their body, as opposed to their previous appearances where they were smoother. When Cuttlefish tries to contact Agent 1 and Agent 2 to come pick them up, DJ Octavio intervenes, but Cuttlefish dismisses it as his radio being broken.

After reaching the center of the Crater, DJ Octavio appears in his battle mech named the Octobot King L3.Gs, trying to confront the two for the recent disappearance of his Octarian army, but when asked about the stolen Great Zapfish, states that he does not even know about it this time, and engages Agent 3 in a fight. Upon being defeated, Octavio tells Cuttlefish and Agent 3 that he indeed did not steal the Great Zapfish, and Cuttlefish thinks that someone else might have done it, but before they can continue, the ground beneath them collapses as Fuzzy Ooze flows out. A piece of Ooze takes Cuttlefish away from Agent 3, who loses their Hero's Suit and Power Eggs in the fall. Agent 3 then wakes up in Alterna, where they are greeted by the New Squidbeak Splatoon comprised of the old Agent 3 (now Captain) and the Squid Sisters.

The new Agent 3 is also aided by a robotic assistant named O.R.C.A., who helps guide them through Alterna.

At the end of Site 1, Future Utopia Island, Deep Cut makes their entrance and makes it clear that all the loot in Alterna belongs to them. Later, each of them guards one of the three 'treasures' in the area and Agent 3 has to defeat them to continue.

After collecting all three parts of the Treasure, Callie and Marie assemble it into a lawn mower-like tool, which the Captain uses to cut off the fur near the rocket at Alterna Space Center so the team can go there and save Cuttlefish.

The Captain gets hurt while using the tool, and it also breaks down. Soon after this, Deep Cut appears again trying to take back the treasure, but Marie tells Deep Cut that they do not need the treasure and that they can have it back. Deep Cut then asks Marie to be their boss, who reluctantly accepts.

On their way to the rocket, the party overhears that Mr. Grizz plans to use Cuttlefish and the Golden Eggs (collected by the unwitting Inklings and Octolings in Inkopolis and Splatsville working in his company) to 'restore the balance of the world'. When asked about the reason for hunting treasures, Shiver and Frye explain that they want to sell the treasure to help those in need in Splatsville, while leaving little to themselves, which makes Callie and Marie respect them.

After completing all the sites, Agent 3 has to get on the rocket which is covered by Fuzzy Ooze. Once they get to the top, they and the New Squidbeak Splatoon find Cuttlefish all dried up and lifeless, as a result of being dehydrated by Mr. Grizz. Grizz, now revealed to be a grizzly bear, then appears and escapes on the rocket, which will then spread Fuzzy Ooze all over the Earth and bring forth a new era of mammalian dominance.

The Captain drops a tear on Cuttlefish's body, which makes him come to his senses. Deep Cut appears again and helps Agent 3 and Smallfry reach Mr. Grizz's rocket. There, Agent 3 and Mr. Grizz engage in a fight. After having some of his Fuzzballs splatted, Mr. Grizz knocks Agent 3 and Smallfry out from his rocket as he absorbs the Fuzzy Ooze and plans to send it on the Earth himself. Soon, DJ Octavio, now knowing who the true culprit is, appears in his modified Octobot to save the two. DJ Octavio, the Squid Sisters and Deep Cut then play the Calamari Inkantation 3MIX together, and Smallfry becomes Hugefry shorty after that, who then fights Mr. Grizz as DJ Octavio and Agent 3 vacuum the Fuzzballs on Mr. Grizz's body, before blasting him back with the ooze, defeating him. After emerging victorious, DJ Octavio, Agent 3 and Smallfry return to the Earth together.

Mechanics
Comparing to the Hero Mode of the previous two games, Return of the Mammalians has a less linear progression similar to the Octo Expansion. Upon entering a mission, O.R.C.A. explains the rule of the level with dialogue and prompts the player to select one of the sets of weapons available. Different sets of weapons may have different Power Eggs rewards. Some missions also cost Power Eggs to play, and/or have special conditions that will cause the player to get splatted if they fail.

The areas in this mode are covered in Fuzzy Ooze, which serves as the obstacle blocking the path to other areas, rather than having the missions locked themselves. The player needs to use the Power Eggs they collect from the missions to clear them in order or progress.

The map screen in each of the sites tracks how many of each type of item the player has found on the overworld (loot anchors that contain decorations, golden records, Sardinium, and Sunken Scrolls). The map highlights areas with unobtained items to find in green, labeled as Areas of Interest, whereas it marks areas which the player hasn't been to yet with black striped squares labeled Parts Unknown. If the player fully collects all items in a site and goes to every possible part of the map so that there are no longer any black squares, the site becomes marked as "Surveyed". Marie will award the player with a piece of the map of Alterna as a sticker if they survey that site.

Fully surveying all sites causes a Shel-drone to appear. Each day the player can charge this drone by using 999 power eggs. The following day, the drone will send an item to the lobby terminal. These items include Tableturf Battle card packs, and meal tickets, as well as decorations that can only be found in Alterna. This is currently the only way to get duplicates of these decorations. If the Shel-drone doesn't appear after the player surveys every area, they will need to go back to Splatsville and Alterna again.

Missions
Prologue: The Crater 



Site 1: Future Utopia Island 



Site 2: Cozy & Safe Factory 



Site 3: Cryogenic Hopetown 



Site 4: Landfill Dreamland 



Site 5: Eco-Forest Treehills 



Site 6: Happiness Research Lab 



Finale: Alterna Space Center  

Regular enemies
This table is sorted by order of appearance. Enemies marked with * are newly introduced in.

Quotes
"SRL historian here with a pro tip. Want to learn about the weird world of Alterna AND brush up your skills with all kinds of weapons and varied terrain? Check out Story Mode! Just follow the strange old man into the Splatsville sewer to get started. Wow, new sentence.

Another Story Mode tip: most stages allow you to choose from multiple weapon loadouts. So you can sharpen your skills AND take advantage of a weapon's particular strengths to survive. That said, sometimes you'll have nothing to rely on but your wits... and maybe a Zipcaster."

- @SplatoonNA on Twitter

"It's not all multiplayer mayhem in #Splatoon3, you know? Dozens of single-player stages filled with unique tricks, tests and... hairy Octarians await in Story Mode."

- @NintendoEurope on Twitter

Trivia

 * This is the only single-player campaign that does not have "Octo" as the first word.
 * This is the first single-player campaign to not include any missions based on any Turf War stages.
 * This is also the first single-player campaign to involve and have the player to go into space.
 * Agent 3 has two styles of the Hero Suit. A post on Nintendo's official website hinted that they are "each suited to different situations".
 * In game it turns out that the torn down version is a "standard" form while the other is part of the upgradable Hero set.
 * Unlike Octo Valley and Octo Canyon, the player can use a non-hero weapon in this campaign.
 * Additionally, this story mode bears multiple similarities to the Octo Expansion:
 * The player can choose between different non-Hero weapons.
 * Both modes have a similar interface, a variety of mission conditions and heightened freedom as opposed to the previous two Story Modes' linear progression.
 * Both modes have a form of currency that is used to gain access to new areas and missions as well as playing missions (CQ Points and Power Eggs). Not all missions in Return of the Mammalians cost Power Eggs to play, and instead, Power Eggs are primarily used to clear Fuzzy Ooze that block the way.
 * Both modes have a key NPC that, besides guiding the player throughout the area, will also splat them if they fail certain objectives or missions (such as running out of ink). They are C.Q. Cumber and O.R.C.A. respectively.
 * Both modes have a final part that has multiple continuous stages before the Final Boss. They are the Deepsea Metro Escape and Alterna Space Center respectively.
 * Both modes are underground the normal sea level.
 * The player is not equipped with their weapons at the beginning of either part (Coccyx Phase and Villi Phase for the former and Alterna Space Center: Entrance for the latter), and must find them within the stage.
 * Both parts have a section (Diaphragm Phase and The Spirit Lifter: First Class) that provides unlimited use of a particular special weapon (Inkjet and Zipcaster).
 * Both of these sequences feature two songs written by the game's main idol group, playing throughout every section except the first one and the last two.
 * The final mission (Turf War and Return of the Mammalians respectively) of both modes have the player stop the antagonist within a time limit.
 * Failing either of these by either being splatted or running out of time will show an additional cutscene of the world being destroyed before showing the usual 'Continue?' screen.
 * In both cases, the successful final attack (Pearl's Princess Cannon and DJ Octavio's vac spit) eventually grow so powerful that they damage the game UI in some way.
 * Both share their name with a playable game mode.
 * Octolings are playable in the single-player campaign of the base game for the first time.
 * After beating the Story Mode, the statue of Mr. Grizz at Grizzco is replaced by a fish with a bear in its mouth, modeled after Smallfry (in its Hugefry form) and a smaller Mr. Grizz. The original statue is located behind the camp of the New Squidbeak Splatoon and can be interacted with to replay the final section.
 * Before Version 1.1.1, if the player closed the game or entered sleep mode during Deep Cut's news broadcast directly after beating the final boss, they would be forced to replay the entire final section due to a glitch.
 * Cuttlefish's quotes about Octarians or squid references do not change when the player is an Octoling.
 * Many mysterious sounds can be heard in Alterna, but are hard to hear and are distorted. Extracting the game's audio files has found some of this ambient noise to be announcement messages sent over a somewhat broken-up loudspeaker system to the Alterna Space Center, with various notification sounds and human speech in English reporting on the status of the rocket launch.
 * After completing the final mission, the rocket in the center of Alterna will turn blue.
 * Return of the Mammalians is the second single-player campaign in the Splatoon series to have one or more groups of levels that do not contain a boss level. The first single-player campaign to do this is Octo Expansion.
 * As level progression in Return of the Mammalians is linked to collecting Power Eggs rather than completing levels, the ending can be reached by completing a minimum of 15 levels (the five Crater missions, the three Deep Cut bosses, and the seven stages of the space center and the rocket), the fewest in the series and one less than in the Octo Expansion.