Dark Bowser

"Soon this kingdom will vanish along with all who dwell within. And you, too, will sleep eternally in the dark power's embrace!"

- Dark Bowser

Dark Bowser is Bowser's final boss in Mario & Luigi: Bowser's Inside Story. He has all the powers Bowser has, along with many dark powers. He is far more evil than the original Bowser; while Bowser simply desires to take over the Mushroom Kingdom, Dark Bowser wants to destroy it outright.

Mario & Luigi: Bowser's Inside Story
While the evil Dark Star was gathering DNA from Bowser's body, Mario and Luigi tried to stop it before it succeeded. The brothers manage to defeat it, but it seems that it had already got every piece of DNA that it needs. The only parts missing were the legs, which it gathers by inhaling Dark Fawful, thus creating a dark version of Bowser. He flees from Bowser, but when Bowser finds him in the secret tower, they both breathe fire at the same time, starting a duel. Bowser overwhelms him, then they both curl up into a spike ball and the fight commences. Bowser again overwhelms his dark form, who then covers the whole Mushroom Kingdom in darkness, with Bowser being the only one who could defeat him. Eventually, sick of the battle of the titans, Bowser charges up his fists and gives the dark version the final blow.

One of Dark Bowser's attacks is throwing a boulder into the air and blasting it apart, causing rocks to fall out of the sky. Bowser must use his shell to avoid taking damage. However, he must also punch one of the rocks at Dark Bowser, who is charging an attack. When the rock lands in his mouth, it plugs him up and causes his attack to damage himself from the inside. If Bowser does not, he is blasted by dark fire.

Another attack involves him punching Bowser repeatedly. Bowser must counter with his own punch, making their fists clash. The two giant blows meet and throw the titans back, creating a shock wave. Then Dark Bowser will jump into the air as a spiked ball and tries to land on Bowser. Bowser must retract into his shell to avoid taking damage. He can then counterattack by quickly throwing a punch at Dark Bowser. Another attack traps Bowser in a cage and raises it into the sky. He will then charge up an energy ball. Bowser must try and destroy the cage's lock before he gets hit by the energy ball. He can also swing the cage off its hinges with shell defense to damage Dark Bowser. After taking enough damage, Dark Bowser will fall to the ground; he is then healed by the ingested Dark Fawful and will grow larger. He will always follow this up by tossing a mixed ball of "Dark Minions" at Bowser, including Goombas, Koopa Troopa, Thwomps, Bob-ombs, and Bullet Bills. The ball pushes Bowser back several feet, after which he must then walk back through the "Dark Minions" while dodging or countering their attacks. When he catches up, Dark Bowser again curls up into a spike ball and tries to body slam him. Bowser must curl up into his shell, then do it again as Dark Bowser prepares the next body slam.

Bowser has to punch him in the stomach so that he spits up Fawful and then inhales him, which Dark Bowser will try to do as well. Successfully inhaling Fawful pulls him into Bowser, where the Mario Brothers must fight Dark Fawful. Only upon Dark Fawful's defeat can Bowser give his shadowy doppelganger the final blow.

Once defeated, Dark Bowser dissolved, leaving only the Dark Star, which rose into the air and exploded, restoring the Mushroom Kingdom to normal.

While Dark Bowser is incomplete, he speaks extremely slowly. However, as he becomes complete, he starts to speak fully. In the Japanese version, his speech is halted and written completely in katakana while he is incomplete. When Dark Bowser inhales Dark Fawful and is completed, he begins to speak in more natural Japanese, with kanji and no pauses.

Trivia

 * Dark Bowser is the third final boss that Bowser has a direct hand in defeating, after Smithy and Super Dimentio from Super Mario RPG: Legend of the Seven Stars and Super Paper Mario, respectively (although using Bowser for either of these battles was optional). The Mario Bros. also defeated Elder Princess Shroob, from Mario & Luigi: Partners in Time, by deflecting Bowser's fireballs up at her (Bowser was unknowingly possessed by the alien princess and she was using him to try and defeat the Mario Bros.).
 * Bowser's fight with Dark Bowser is reminiscent of the final battle in Paper Mario, as both take place on a large circular arena above Princess Peach's castle.
 * In the North American version, while Dark Bowser is plugged up, he will grow and shake, whereas in the Japanese version, he just grows.
 * Like Chakron, when Dark Bowser is defeated, he offers no EXP.
 * Dark Bowser, along with the Dark Star Core, is the only boss that can be fought multiple times on the same save file. There is no Save Block after defeating Dark Bowser, so the player can commence the battle again.
 * Dark Bowser is the third final boss that is a different form of Bowser, the first two being Bowletta and Shrowser.
 * Surprisingly, those forms of Bowser are all in the Mario & Luigi Series games.
 * This is the second time the evil spirit of the main antagonist was fought inside Bowser's body. The first time was in Mario & Luigi Superstar Saga against Cackletta's Soul inside of Bowletta's mouth, as proven by the teeth and the flames.