The boss is Shiver, who rides on her megalodon Master Mega, a large shark with a saddle and rocket boosters.
Walkthrough
Note: Due to the level having no fee, you may retry from checkpoints as many times as you want, even if you lose all your lives.
First Phase
Shiver and Master Mega will circle the water surrounding the central platform, occasionally leaping out to fire vertical slashes of ink similar to those of a charged Splatana or charging straight at the player, the previous breaking armor on contact and the latter similar to the Reefslider. While they can be attacked in this state, their constant movement makes them difficult targets. Instead, the player should wait for them to try and attack from below and place a bomb (or Smallfry) in the spot they will strike as if fighting a Maws; throwing a bomb into Master Mega's open mouth the moment before he charges is also effective.
Should Master Mega swallow a bomb or Smallfry, he will fly onto the platform and leave itself open as it slowly crawls back to the water. After taking enough damage, Shiver will fall off Master Mega and can be splatted to begin the next phase.
Second Phase
Shiver and Master Mega will now create ink tornadoes, leaping from one tornado to another to confuse the player before firing a beam of ink straight forward. Master Mega leaves its mouth open for a moment after performing this attack, and throwing a bomb (or Smallfry) into its mouth will knock it onto the platform. After dismounting Shiver and splatting her a second time, the third phase will begin.
Third Phase
The beam attack now fires three beams, one after the other. Additionally, Master Mega will crawl faster, reducing the amount of time it can be damaged while it is stranded on the platform. Splatting Shiver once more will end the battle.
Stop where you are. After the treasure? You have excellent taste. But you're too delicate to claim this particular item. Don't you agree? Ah, I see. The cold-shoulder routine. Guess you're pretty wicked after all. We'll have to teach you some manners. Join me, Master Mega!
”
“
Pedal to the megalodon!
”
Before the battle (rematch):
“
Stop where you are. You're back, which can only mean... you missed me! How sweet of you, coming all this way just to give me a win. Ahhh, the cold shoulder again. You grow more wicked with every battle... And that's supposed to be MY thing. Another lesson, Master Mega!
”
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Pedal to the megalodon! AGAIN!
”
During the battle:
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Share your wisdom, Master Mega!
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We'll shred you this time for sure!
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Time to feed the fish! Hahaha!
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Master! Get us back in the water! NOW!
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“
You're pretty tough... for an appetizer. Master! I need you to REALLY focus this time, OK? Attaboy, Master Mega! Let's FINish this!
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“
That was just a rehearsal. The real show starts NOW!
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Let's swirl things up - way, WAY up! Haha!
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Awaaay we go!
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OK, Master Mega. Show your pearly BITES!
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UGH! Master! Get it together!
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“
Oh, come on! What is WITH you?! Master, you had better get serious... or else! Yeah! That's more like it! Time to show you our REAL power!
”
“
PEDAL - and I mean it this time - TO THE MEGALODON!
”
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Can you handle THIS?!
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“
Ugh. Stop embarrassing me, Master!
”
After the battle:
“
Owww... I think that's enough of a lesson for today... But you haven't seen the last of Deep Cut. Until next time. Huh? OH N-
”
After defeating the boss:
Agent 2
Good work, Agent 3.
Agent 2
I mean, we didn't find Gramps, but we found another "treasure." That's something!
Cuttlefish
Ksss-ksssh! Kssssssht!
Cuttlefish
...Do you read me? Come in!
Agent 1
Gramps is on the line! Hellooo, Gramps!
Cuttlefish
Oh, Agent 1! Good to hear your voice.
Cuttlefish
I'm, uh...still locked in some kinda room. Finding the exit is like lookin' for a needlefish in a coral reef!
Cuttlefish
OH! I mean, oh... I better shout whisper. SOMEONE'S COMING!
???
Ah. You've woken from your hibernation, have you? CUTTLEFISH!
Cuttlefish
Hmph! That's, uh...former CAP'N Cuttlefish to... whoever you are!
Cuttlefish
...Who ARE you, anyhow? Identify yourself!
???
Grrrahahaha! You're lively for an old bag of... Does your species have bones? No matter!
???
You can call me... Mr. Grizz.
Cuttlefish
...izz? Ksss-ksssh! ...know any Grizz... Ksss-ksssh! ...mister or otherwise!
Cuttlefish
KSSSSSSHT!
Agent 1
Nooo! It was getting so good! Gramps? Are you still there?
Agent 1
Argh! I think we lost him. But we'll find him for real if we keep tracking the signal.
Agent 1
That's all you, Agent 3. Let's go!
Gallery
The weapon selection screen.
The battle introduction.
Shiver's ink color in Return of the Mammalians.
Shiver when Color Lock is enabled.
End screen for the first clear of the stage, featuring a part of the Treasure.
End screen for subsequent clears of the stage, featuring a silhouetted part of the Treasure.
Trivia
Similarly to the final bosses of Octo Valley and Octo Canyon, some of the character dialogue changes on repeat playthroughs.
Shiver's ink color has Deep Cut logos imprinted on it, a trait shared by Frye and Big Man.
Etymology
The mission's name is likely a reference to The Lord of the Rings. In this trilogy, the character of Gollum refers to the One Ring as his "precious".