The title of Splatoon 3's single-player DLC released on February 22, 2024, is Side Order.
Side Order is the second half of the paid Splatoon 3 Expansion Pass. Unlike the first wave, which added Inkopolis as an alternative hub area, this expansion adds a substantial new single-player campaign. It was announced during a Nintendo Direct in February 2023 and released for Nintendo Switch on February 22, 2024.
The story follows Agent 8, the Octoling protagonist of Splatoon 2: Octo Expansion, who becomes trapped in the colorless Memverse. Pearl and Marina of Off the Hook return, with Pearl appearing as a helpful drone, while Agent 8 climbs a thirty-floor spire. The campaign introduces roguelite structure: stages are randomized, upgrades can be purchased between attempts, and losing a run sends the player back to the beginning.
A common mix-up is confusing Side Order with Octo Expansion, which is paid DLC for Splatoon 2, or with Splatoon 3's base-game story campaign, Return of the Mammalians. Side Order is specifically the later, roguelite-focused single-player expansion for Splatoon 3.