Splatoon 2/The Showdown

The Boss Kettle for this mission can be found directly in the middle of Suction-Cup Lookout, under the kettle for Spinning Campground.

Walkthrough
To defeat the Octo Samurai, you must splat it to make it drop its Dynamo Roller and its belt on the ground. All areas except the back are vulnerable. The roller grows into a larger form and a tentacle pops out of the belt left behind. Attack the tentacle 3 times to defeat the boss.

Phase 1
The boss will similarly fling its Roller to Inklings but has a very wide range. The Samurai can also get on top of his weapon and charge towards the player, leaving behind a wide trail of ink. If he gets a direct hit, it's an instant Splat. The boss takes a break every time he does this, letting the player get in free hits. He always does a backward jump before doing his charge attack.

Phase 2
The Octo Samurai does everything he does from phase 1, but he has two new attacks:
 * He jumps towards the player and does a vertical swing with his roller.
 * He quickly spins around with his roller leaving a circle formation of ink. A direct hit is an instant splat. Before performing this attack, his eyes give off a distinctive shine.

Phase 3
Most of his attacks get more vicious, and he uses a new one:
 * The Octo Samurai starts off performing three, extremely long-ranged vertical swings.
 * He chases you when he does his charge attack. He still takes a break after this.
 * He will always swing three times in a row when he does his regular swing.
 * He will always follow up his jump attack with three vertical swings. These swings are not as long-range as his other vertical swing attack.