Alterna and the Last Mammal

Return of the Mammalians is the story mode of Splatoon 3, and its name is a warning. For three games the series had treated mammals as a memory: a cat in a capsule, a skeleton on a scroll. Splatoon 3 brought one back, and used him to tell the saddest story in the series' history.

Descending into Alterna

The new Agent 3, recruited by Cap'n Cuttlefish at the edge of the Crater outside Splatsville, descends with a Smallfry companion and finds the Cap'n missing and the Great Zapfish gone. At the bottom of the Crater is Alterna: a vast underground cavern with an artificial sky, crystalline structures, and the ruins of a human settlement. It is beautiful and utterly wrong. Everything is coated in a growing, hairy substance the game calls Fuzzy Ooze, and Octarians who touched it have become fuzzy, mindless versions of themselves.

The New Squidbeak Splatoon, now including Callie and Marie as Agents 1 and 2 and the original Agent 3 as its captain, sets up camp and begins clearing sites. Each site is a level, each level hides an Alterna Log, and the logs, read in order, tell you what this place was.

The logs

The Alterna Logs are written by the humans who built the refuge. After the seas rose, a group of survivors retreated underground and constructed Alterna as a sealed city. They could not see the sky, so they made one: a ceiling of liquid crystal that could display any image the residents imagined. For a time, it worked. Generations grew up under a painted heaven.

But the crystal sky was a comfort, not a solution. The logs describe a growing longing for the real surface, and a plan to reach it not by climbing but by leaving: the residents began building rockets. They tested one by launching an animal into space. That animal was a bear. The logs record the launch as a success. What they record next is that the liquid crystal sky, which responded to the residents' thoughts, became unstable under the weight of their yearning. In the final entries, the crystals fall. The logs end.

It is the only time the series lets humans speak for themselves at length, and it lands like a punch. The people of Alterna did not die in the flood. They died of wanting to go home.

They built a sky so they would not miss the real one. It did not work.

The bear

The bear survived. Drifting in space for an unknown span, it eventually returned to Earth and found the world transformed. The humans were gone. The cephalopods ruled. And the bear, who the logs' rocket had made intelligent enough to understand what he had lost, was the last mammal alive.

He took a name: Mr. Grizz. He founded Grizzco Industries, a shady company that hires Inklings and Octolings to collect Salmonid Golden Eggs, and for the whole of Splatoon 2 he spoke only through a wooden bear statue and a radio. Players assumed he was a gruff businessman with a bear fixation. Splatoon 3 revealed him in the flesh, and revealed what the eggs were for.

Return of the Mammalians

Grizz's plan is the Fuzzy Ooze. Made from his own fur, it converts any creature it touches into a fuzzy mammalian thrall. He stole the Great Zapfish to power a rocket, built from Alterna's abandoned technology, that would carry the ooze into orbit and spread it across the whole planet. Every Inkling, every Octoling, every fish would become a mammal. Grizz would no longer be alone.

He also kidnapped Cap'n Cuttlefish and dried him into a shriveled husk to keep him out of the way. Cuttlefish, being Cuttlefish, survived.

The final battle takes place on the launching rocket. Agent 3 climbs it with the whole cast in support: the Squid Sisters on the radio, Deep Cut on the ground, DJ Octavio (freed and briefly allied, piloting his Octobot) providing a ride, and Smallfry, fed on Grizz's fuzz, grown into an enormous Hugefry. With the Calamari Inkantation playing and every idol group singing, Grizz is defeated. His final moments are bitter and strangely dignified: he is not sorry, but he is finished. The rocket falls. The mammals do not return.

Alterna reframes everything. Tartar wanted to erase the sea creatures because they were unworthy of humanity's knowledge. Grizz wanted to overwrite them because he could not stand being the only one of his kind. Both are creatures of the old world who cannot accept the new one. The Inklings, who have no idea what they inherited, keep beating them because they are not fighting for the past.

And there is a quieter note. Alterna's residents wanted the sky. Agent 3, at the end of the game, stands on the surface of the Splatlands under the real one. The humans never got there. The kids who came after did, and they use it to play.