Dark Bowser

Bowser against Dark Bowser, who is fully powered up by Dark Fawful.

Dark Bowser is Bowser's final boss in Mario & Luigi RPG 3!!!. Dark Bowser covers the entire Mushroom Kingdom in darkness and Bowser faces him.

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 he already got every piece of DNA that he needed, the only part which was missing were the legs which he gathered by inhaling Dark Fawful into his stomach, and thus creating a dark version of Bowser. Dark Bowser then covers the whole Mushroom Kingdom into darkness, and Bowser was the only one who could defeat him. Eventually, after being defeated, Bowser then charges up his fists and gives the dark version the final blow.

One of Dark Bowser's attacks is throwing a meteor 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 punch one of the rocks to Dark Bowser, who is charging an attack. When the rock lands in his mouth, he executes his attack, and the rock causes it to blow up in his face.

Another attack has him punch Bowser repeatedly. Bowser must block a punch with his own punch. Then Dark Bowser will jump into the air and Bowser has to hide in his shell to avoid taking damage from Dark Bowser, who's falling out of the sky. Another attack is trapping Bowser in a cage and putting the cage in the sky. He will then charge up an energy ball. Bowser must try and destroy the cage before he gets hit by the energy ball.

At one point, Dark Bowser gets healed and will grow giant. Bowser has to punch him in the stomach so that Dark Fawful will come out of his stomach and make him turn to his normal size.

When Dark Bowser is incomplete, his speech is halting and written in all katakana. When he inhales Dark Fawful and is completed, he begins to speak in more natural Japanese, with kanji and no pauses.