The Knautilus is Baron K. Roolenstein's submarine docked in Krematoa in Donkey Kong Country 3: Dixie Kong's Double Trouble!. The Knautilus is a green fish-shaped vehicle and is where the second and final boss battle against Baron K. Roolenstein takes place. It is likely named after the Nautilus, a submarine from the novels Twenty Thousand Leagues Under the Sea and The Mysterious Island.
The interior of the Knautilus has a large conveyor belt on the floor, as well as a cannon that can launch fireballs. On each side, there are two large, circular devices capable of discharging electricity.
Dixie Kong and Kiddy Kong can enter the Knautilus once they complete every Lost World level. With the five cogs, Boomer activates his machine, causing Krematoa to steam and its waters turn red. The Knautilus's anchor was from the heat, causing it to emerge from the lake.
Dixie and Kiddy go into the center of the lake, where the Knautilus emerged, and enter inside. The final boss battle starts as both Kongs fall onto a conveyor belt area, with electrical machines on each side. They discover Baron K. Roolenstein, who is in the foreground, upset that Dixie and Kiddy uncovered the Knautilus. During the battle, Baron K. Roolenstein controls the electrical machines. If the Kongs successfully avoid the machines, a Steel Barrel appears and a big vacuum in the roof opens. With timing, Dixie and Kiddy can damage Baron K. Roolenstein, by throwing the Steel Barrel up the vacuum, causing it to land onto Baron K. Roolenstein's propeller pack. After being hit enough times, Baron K. Roolenstein is defeated again, and the Kongs are rewarded a DK Coin (in the SNES version) or Bear Coin (in the GBA version), unlike other bosses, which reward a Bonus Coin.
The Knautilus also appears in the opening cinematic of the game's Game Boy Advance remake, where it appears just before the game's title screen; here, the Knautilus opens its front end just before propelling itself at the screen. It could be a depiction of how Donkey Kong and Diddy Kong were captured by the Kremlings, since the intro starts from the perspective of a diving mask, which ends with the Knautilus closing in and "swallowing" the camera, followed by the next shot where the Knautilus rises out of the water.
The battle starts with Baron K. Roolenstein pressing a remote control. This activates the upper electrical device, which discharges blue electricity between the left and right sides, while a cannon in the background shoots fireballs back and forth to the Kongs' path. The Kongs must not jump while the upper electrical device is active. When the electricity stops running, the lead Kong can attack Baron K. Roolenstein by throwing a Steel Barrel into a vacuum on the ceiling if Baron K. Roolenstein is close to the center of the background. This causes the Steel Barrel to land on him. Baron K. Roolenstein flies up the chute and lands into the main arena where the Kongs are.
Baron K. Roolenstein starts moving back and forth in a set pattern. When he approaches either the left or right corner of the arena, the Kongs must jump onto the electrical machines while they are inactive. To attack Baron K. Roolenstein, Dixie or Kiddy must throw a Steel Barrel at his helicopter pack. After taking two hits, Baron K. Roolenstein moves back into the background and reactivates the cannon and the upper electrical machine. When it stops again, the Kongs must throw another Steel Barrel through the chute to hit Baron K. Roolenstein a fourth time. The process is repeated another time.
When Baron K. Roolenstein takes a fifth hit, he reactivates the electricity and cannon as usual, except the conveyor belt starts moving left then right repeatedly. The Kongs must avoid running into the lower, circular electric platforms or otherwise they take damage. Upon taking a sixth hit, Baron K. Roolenstein presses his remote again to reactivate his machines, but then hovers up the chute and back into the main arena again. Baron K. Roolenstein presses his remote again, causing a small ray of electricity to approach the Kongs from either of the bottom electrical machines.
As the electrical ray approaches Dixie and Kiddy, they must go behind the Steel Barrel, which absorbs the electricity. The Steel Barrel is surrounded by electricity for a few seconds before it disappears. Baron K. Roolenstein's machines deactivate at the same time, giving the Kongs the opportunity to jump and throw a Steel Barrel up to Baron K. Roolenstein's helicopter pack. The electrical machines reactivate, along with an electrical beam which the Steel Barrel must absorb again. The machines deactivate quicker than the previous time, and the Kongs must throw another Steel Barrel at Baron K. Roolenstein's helicopter pack. He then activates the machines again, this time along with the conveyor belt on the floor. After the machines deactivate, Dixie and Kiddy must attack Baron K. Roolenstein with another Steel Barrel. The process repeats again. Once Baron K. Roolenstein takes a tenth hit, he is defeated, as shown in the background as he spirals out of control on the Knautilus's steering wheel. Dixie and Kiddy are rewarded a DK Coin or Bear Coin, and they leave the Knautilus.
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