What is the name of the secret boss in Octo Expansion?

The secret boss in Octo Expansion is Inner Agent 3.

Inner Agent 3 is an optional post-game boss encounter in Splatoon 2’s Octo Expansion downloadable campaign. The battle is designed as an extreme test of movement, aiming, ink management, and reaction speed, making it substantially tougher than the campaign’s standard stages and bosses.

To reach the fight, players must clear all 80 Octo Expansion courses without simply skipping the challenges. Completing the full set unlocks the hidden encounter through the campaign’s subway system. Inner Agent 3 is presented as a mysterious, highly skilled opponent connected to Agent 3, which gives the fight both gameplay significance and a strong lore connection to the wider Splatoon story.

The other choices are ordinary Octo Expansion characters or locations rather than the secret boss. Octarian refers to the enemy species, while Iso Padre and C.Q. Cumber are named characters encountered during the campaign. Inner Agent 3 is the distinctive boss name quiz players are expected to recall.