|“||It was not benevolent. It was a frightful star that hid a great evil.||„|
|~ Princess Peach, explaining about the Dark Star|
The Dark Star is an archaic artifact of ultimate power that was sealed away beneath Toad Town and the Bigger Bad of the video game Mario & Luigi: Bowser's Inside Story, working in a parasitic relationship with Fawful.
It first begins with Fawful finding it, unknowingly, Fawful has no idea it has a living entity within and believed it was a harmless artifact of power. He puts the Dark Star onto a machine to absorb the energy of it's power. Bowser comes by later to stop Fawful and defeats Midbus, Fawful's assistant, and the Dark Star falls off the machine from the battle, the Dark Star then inspects and jumps inside Bowser's body. While in his body, the Dark Star absorbs Bowser's DNA and gains his abilities (flame breath, super strong punches, etc). After a tough battle with Mario and Luigi (inside Bowser's body), the Dark Star possesses Fawful and turns him into Dark Fawful. Later though, Bowser defeats Dark Fawful and he turns into Dark Fawful Bug, and is absorbed by the Dark Star. In the end the when Dark Fawful is defeated, the Dark Star loses its power and Bower finishes it off for the final time is destroyed.
Although the Dark Star does not speak at all (Except when it has a body of it's own), it does show it's hatred and anger throughout the game. Never changing the expression that it shows. It shows it's hate by attempting to destroy the Mushroom Kingdom and it's citizens. It is noted, that when the tide of the battle changes in favor of the player, the Dark Star still has it's expression of hate and anger, not expressing disbelief of losing the battle. This makes people believe that the Dark Star may only experience two feelings: anger and hate. The Dark Star's power is so hate filled and evil, that Bowser's body couldn't even handle it, Bowser tried to devour it to gain its power, but it caused severe pain to his body.
The Dark star never really had a plan to begin with, as it was sealed away beneath Toad Town, but when Fawful finds out about it, everything changes. It begins formulating a plan, and in doing so, unintentionally creates Dark Bowser. It awakened when Fawful built a machine to absorb all of it's power but after Midbus, Fawful's assistant, was defeated he was stopped when Bowser punches him out of the way. Even with half of the Dark Star's power though he transforms into Dark Fawful. At the same time the Dark Star sees this as a chance to enter Bowser's body. When Starlow sees it, he immediately tells the Mario Bros. to stop it.
When the Mario Bros. catch up to the Dark Star, its absorbing Bowser's DNA and starting to acquire some of his abilities and becoming Dark Bowser, they finally have a battle and they defeat it. It exits Bowser's body to say that even with Bowser's dark power, it is still missing the power Fawful took, you can tell because it doesn't have legs so it looks like a ghost. It heads off to find him, but Bowser finds Dark Fawful who is also trying to recapture the Dark Star for the rest of his power. Bowser and Dark Fawful have their last battle and Dark Fawful loses, and turns into a weaker form, Dark Fawful Bug. Starlow says that if the Dark Bowser finds it, then there will be no hope to defeat it.
Unfortunately, it runs off to be sucked up by Dark Bowser, creating the complete Dark Bowser, which becomes more powerful than Bowser could be. It escapes to the top of Peaches Castle with Bowser in pursuit, and finally Bowser fights Dark Bowser at the very highest point. Dark Bowser then opens his mouth and unleashes a Dark Hurricane, engulfing the entire Mushroom Kingdom with all the residents helplessly being flung in it. During the battle when Bowser defeats Dark Bowser, the Dark Fawful Bug will revive him and become Super Dark Bowser. This is when Bowser can knock the Dark Fawful Bug out of Super Dark Bowser and suck him up.
The Dark Fawful Bug enters Bowser's body and the Mario Bros. fight it. It too becomes a much bigger more bigger and scarier form. When they destroy his legs, the Dark Star emerges from the Dark Fawful Bug's body, becoming an antenna/Dark Star Core. The Mario Bros. defeat the Dark Star Core and the energy source for Dark Bowser. Bowser sees this and ends it with a couple of his KO Finale Punches. After that, the Dark Bowser cannot believe what happened and reverts to Dark Star and flies into the sky exploding and turns everything to normal.