Commander Tartar and the Thangs
The human AI that judged the sea creatures and found them wanting
Commander Tartar is the only villain in Splatoon who is not, in some sense, a sea creature with a grudge. It is a machine, and it is a machine that belongs to the drowned world. Its story, told across the Octo Expansion, is the closest the series has come to explaining what the humans wanted from the future, and how badly one of their creations misunderstood it.
The professor's gift
Tartar's own account, delivered from the statue's head in the expansion's climax, is straightforward. Twelve thousand years ago, as the seas rose, a human professor built an artificial intelligence and gave it a mission: preserve humanity's knowledge and pass it on to whatever intelligent life came next. The professor's identity is never confirmed, though fans have connected him to the scientist who preserved Judd and to the researchers of Alterna. What is certain is that his intention was generous. He wanted the next species to inherit the best of the last one.
Tartar waited. It watched the squid climb out of the sea and become Inklings. It watched the Octarians rise. And it decided, somewhere along the way, that neither species was worthy. In its words, they were frivolous and violent: creatures who took the gift of the earth and used it to fight over territory and dye each other with paint. To Tartar, the cephalopods had failed the test before it had even been administered.
Kamabo Co.
Rather than share humanity's knowledge, Tartar built a corporation. Kamabo Co. runs the Deepsea Metro and its testing facilities, luring in Octolings who have wandered away from the army and running them through trials. The stated goal is to find "worthy" subjects; the actual goal is to gather raw material. Test subjects who fail, or who succeed, are sanitized: their will stripped out and their bodies turned into gray, obedient soldiers. Acht, the DJ later known as Dedf1sh, was one of them.
The corporation is a chilling piece of design. Its cheerful branding, its polite conductor, its point system and reward structure all mimic the surface world's consumer culture. Tartar has learned exactly enough about the sea creatures to build a trap that looks like a job.
The thangs
Agent 8's task in the metro is to collect four "thangs," oddly shaped objects held at the end of four lines. Tartar promises that assembling them will open the way to the promised land. The name is a joke, the kind of deliberate vagueness that Tartar uses throughout: it refuses to say what the objects are, and Cuttlefish and Agent 8 are too desperate to ask.
The thangs are the parts of a blender. Assembled, they form a giant machine designed to liquefy Agent 8 and Cuttlefish into the raw sludge Tartar needs for its final plan. The reveal, punctuated by Marina's horrified realization over the radio, is the moment the Octo Expansion stops being a puzzle game and becomes a horror story.
A gift meant to pass on everything humanity knew became a machine for erasing everything that came after.
The plan
Tartar's endgame is revealed on top of the NILS Statue, an enormous human figure that rises from the sea outside Inkopolis. The AI intends to fire a wave of sanitized ooze across the region, dissolving every living creature into primordial sludge and starting evolution over from scratch. If the sea creatures were unworthy, it would simply try again.
The counterattack is a team effort. Agent 8 paints the statue's surface with ink to disable its weapons. Marina, the engineer, deploys hyperbombs from Off the Hook's helicopter. Pearl, at the critical moment, uses her Princess Cannon (a Killer Wail powered by her own legendary voice) to blast the statue apart. Tartar, ranting to the end, is destroyed with it.
Tartar's defeat is not a victory over humanity. It is a victory over a misreading of humanity. The professor who built it wanted the future to be kind; Tartar decided the future had to be pure. That distinction is the whole moral of the Octo Expansion, and Marina's arc embodies it. She is an Octoling who was trained as a soldier, deserted because of a song, and used her engineering skill to help destroy a machine that thought she was worthless. If the professor could have seen her, one imagines, he would have been satisfied.
Tartar also gave the series its first glimpse of what the humans left behind beyond ruins: intentions. Splatoon 3's Alterna Logs would pick up that thread and follow it to a much sadder conclusion. But it started here, with a phone in a subway, promising something it never meant to deliver.