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 with its goal. The brothers succeeded to defeat it, but it seemed that it already got every piece of DNA that it needed. The only part which was missing were the legs which he gathers by inhaling Dark Fawful, and thus creating a dark version of Bowser. He flees from Bowser, but when when Bowser finds him in the secret tower, they both breathe fire at the same time, starting an epic 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 & causes his attack to damage him from the inside. If he does not, then 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 counter attack by quickly throwing a punch at Dark Bowser. Another attack is trapping Bowser in a cage and raising 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, but then gets healed by the ingested Dark Fawful and will grow giant. He will always follow this up by tossing a mixed ball of "Dark Minions" at Bowser, including Goombas, Koopas, Thwomps, Bob-ombs and Bullet Bills. Bowser must then walk back through the "Dark Minions", back to Dark Bowser. 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 inhale him, which Dark Bowser will try to do as well. Inside, the Mario Brothers must fight Dark Fawful, only after which can Bowser give his doppelganger the final blow.

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

When Dark Bowser is incomplete, he speaks extremely slowly. However, as he transforms into his final form, he starts to speak fully. In the Japanese version, his speech is halting and written in all katakana when 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.

Quotes
Main article: List of Quotes in Mario & Luigi: Bowser's Inside Story

Trivia

 * Dark Bowser is the fourth final boss to be directly destroyed by Bowser (and indirectly by the Mario Bros., as they were the ones who destroyed his core). The first are Smithy and Super Dimentio from Super Mario RPG: Legend of the Seven Stars and Super Paper Mario (although using him for either of these battles was optional), while the third was Elder Princess Shroob from Mario & Luigi: Partners in Time, whom Bowser (as Shrowser, and unaware of her presence) inadvertently deflected his fireballs when the Mario Bros. reflected them back at him.
 * 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.