- This article is about the boss in Mario & Luigi: Bowser's Inside Story. For the final stage in Kirby 64, see Dark Star (Kirby).
The Dark Star was a sentient, evil orb in the game Mario & Luigi: Bowser's Inside Story. It was a rather large blue orb, with a black star with glowing red eyes on the front. The toads dug up the dark star while building Toadtown, wakening it from a deep sleep. The dark star went on to terrorize the world, until it was finally defeated by the Star Sprites. The Star Sprites then sealed the dark star beneath Toadtown in a seal that could only be broken by Princess Peach.
After conquering the Mushroom Kingdom, Fawful began to hunger for more power when he heard about the dark star's powers. He kidnapped the princess and destroyed the seal. He then used a machine to drain energy from Peach to awaken the dark star. While the dark star began to awaken, he used its power to create a blockade in front of the castle to prevent anyone from coming, but Mario and Luigi were able to find the three Star Cures and destroy the blockade. Bowser was then able to storm the castle and found Fawful, Midbus, the princess, and the dark star. Midbus distracted Bowser while the dark star awakened by challenging him to a battle. After Bowser had beaten Midbus, the dark star finally awakened. Fawful used a vacuum helmet to drain the dark star's energy, but only got a small amount of it, because Bowser then punched him out of screen view. As Bowser began to laugh, the dark star flew in to his mouth, giving him heart burn. Mario, Luigi, and Starlow chased the dark star through Bowser's mouth. They had almost caught it three times, but the dark star simply absorbed some of Bowser's DNA, then escaped. Eventually, they managed to corner it, leading to a battle. After defeating the dark star, it escaped from Bowser's mouth, but had succeeded in getting what it was after.
After exiting Bowser's mouth in a puff of smoke, the dark star then took the shape of Bowser, but unlike Bowser, he was blue, had glowing red eyes, and had a black mohawk, but was incomplete, due to Fawful draining some of its power. Dark Bowser then searched the castle for Fawful, but the original Bowser found him first. After being defeated, Fawful turned in to an insect-like creature, then fled. In the next room, Dark Bowser found Fawful and inhaled him, completing his form. Bowser chased his counterpart to the top of the castle, finally cornering him. Dark Bowser then unleashed a dark hurricane that imprisoned the entire kingdom, and would eventually cause it to vanish. The two of them then proceeded to the final battle, and ironically, Bowser won. Dark Bowser then returned to the form of the dark star, then exploded, never to terrorize any thing again. The hurricane then vanished, and the kingdom returned to normal.