Spinal Phase

Spinal Phase is the seventh stage in the Octo Expansion finale.

Gameplay
Agent 8 must defeat a partially sanitized Agent 3 in a boss battle.

Agent 3 is armed with their Hero Shot, Splat Bombs, and has a large arsenal of special weapons at their disposal. They always enter the arena by a Super Jump and activate a Splashdown upon landing, with the exception of the Baller phase. Additionally, Agent 3 can dodge roll at any time as if they were using Dualies or Drop Roller. Agent 3 uses the Hero Shot and Splat Bombs in all phases of the fight but uses a single type of special exclusively in each phase. It should also be noted that, like the player, Agent 3 is able to heal themselves over time, accelerated if they swim through their own ink.

If the player gets repeatedly splatted, they have the option to skip this phase, with each splat contributing to 20% Skip Charge, where the following dialogue is displayed:

"After a fiercely fought yet bittersweet battle with the renowned Agent 3, Agent 8 emerged victorious..."

Phase 1
Agent 3 lands onto the stage with a Splashdown. After that, they fight normally. Agent 3 does have access to Curling-Bomb Launcher during this phase whenever their special is charged.

Phase 2
After taking sufficient damage, Agent 3 Super Jumps back to the spawn point on the UFO flying over the arena. Agent 3 Super Jumps into the stage and immediately activate the Baller, trying to corner the player before setting it off. The Baller can be destroyed with sustained fire, however, both layers of the Baller have much higher health than usual. The rest of the battle continues normally, though Agent 3 can activate another Baller once their special is once again charged.

Phase 3
Super Jumping back onto the UFO, Agent 3 remains on top of it, firing off the Sting Ray in between volleys of Hero Shot fire and Splat Bombs. The UFO is difficult to reach with the Octo Shot's fire, though it can be reached while standing on one of the platforms and it is low enough to throw a Splat Bomb on top of it.

Phase 4
Agent 3 in the final phase starts by using the Splashdown three times in a row. There is a period of rest between each Splashdown where Agent 3 is vulnerable, if enough damage is dealt to Agent 3, they dodge roll out and continue into their next Splashdown. Agent 3 can perform their successive Splashdowns again once their special is charged.

English
{{collapse|

S2 Icon Cap'n Cuttlefish.png Cap'n Cuttlefishgreen
"GYAAAH! Agent 8? Help meeee! Agent 3's mind was hijacked by that crazy phone!"

"Agent 8! Get 'em before they get you! Take down Agent 3, and get rid of that weird glowing goo on their head!"

"Don't let the bombs deter you! Atttaaack!"

"Shoot shoot shooooot!"

"Agent 8! Give it everything you've got!"

"Agent 8! Don't mind me - just take out Agent 3!"

"Take cover and catch your breath!"

"It's not over yet!"

"Well done, Agent 8!"

"Untie me at once!"

}}

{{collapse|

S2 Icon Marina 2.png Marinagreen
"That's the central elevator. The battery is in there!"

"Cap'n Cuttlefish's and Agent 3's signals are close!"

"I sure hope the captain and Agent 3 are OK..."

"The heli? You think we need it?!"

"Good point."

"Huh? The elevator..."

"That's Agent 3! But..."

"You've got this, Agent 8!"

"It looks like Agent 3 removed the limiter..."

"Curling-Bomb Launcher!"

"Agent 8! Use bombs!"

"Wait for the moment between Splashdowns!"

"The goo is gone, so it's probably fine..."

}}

{{collapse|

S2 Icon Pearl 2.png Pearlgreen
"You can make it to the surface with this!"

"Maybe they already made it to the surface?"

"Eight! We'll come get you in the chopper, so just wait up there with Cap, OK?"

"There are only so many chances to use it. We can't let it go to waste!"

"Thanks!"

"It stopped! Who's up there?"

"Inkoming!"

"Eiiiight! Attack!"

"Are you serious? This is way too many specials!"

"Keep it under fire!"

"Dodge!"

"Did we do it?!"

"They're gonna use multiple Splashdowns in a row!"

"It looks like Agent 3 is out cold... again. Will they attack you if they wake up?"

}}

Trivia

 * The icons for splatting a player used in multiplayer matches are displayed when Agent 3 is defeated.
 * Agent 3's idle animation differs from the player animation, where they hold their Hero Shot with one hand while their left hand has the fingers curled up except for the index finger and thumb, which are still curved. Concept art illustrates this animation more clearly.
 * The developers revealed that if Agent 8 gets splatted during this phase, they will actually die, because they are not connected to a respawn platform. This means the game goes back in time every time you get splatted during the escapes.