Splatoon 2: Octo Expansion

Splatoon 2: Octo Expansion is a 2018 downloadable content (DLC) expansion pack for the single-player mode of Splatoon 2 (2017), a third-person shooter video game for the Nintendo Switch. Set in an underground rapid transit system named the Deepsea Metro, the DLC follows an amnesiac Octoling, a humanoid octopus, nicknamed Agent 8. After becoming trapped in the Metro alongside former military general Cap'n Cuttlefish, Agent 8 journeys through a multitude of testing facilities, at the direction of a talking Telephone, with the goal of escaping to the surface.

The development of Octo Expansion began shortly after the release of Splatoon 2 on July 21, 2017. Series producer Hisashi Nogami wanted to give players an opportunity to explore previously undeveloped aspects of Splatoon's world—especially those relating to the Octolings—through a story-driven, single-player adventure. The DLC's levels were designed to be more varied and challenging than those of Splatoon 2's regular story campaign. Octo Expansion's visual aesthetics took influence from the popular culture of eras such as the 1980s to elicit a mysterious atmosphere, while its dark, subterranean setting served to set itself apart from the series' colorful world.

Octo Expansion was released on June 13, 2018. It was met with positive reception for its level design, art direction, and story that reviewers said expanded upon the narrative foundations of earlier Splatoon games. Numerous critics deemed it superior to Splatoon 2's regular single-player mode. Many commentators would directly compare gameplay aspects of future Splatoon single-player experiences to Octo Expansion, particularly the base story campaign of Splatoon 3 (2022) and the spin-off title Splatoon Raiders (2026). Much of Octo Expansion's cast, including Agent 8, would reappear in the single-player expansion for Splatoon 3, titled Side Order.