Dark Fawful was created when Fawful absorbed half of the Dark Star's energy. He then started looking for the rest of the dark power. Meanwhile, the dark Star is absorbing Bowser's DNA to form Dark Bowser, the final boss of the game. While looking for the Dark Star, Fawful winds up in the meeting room from the beginning of the game. Bowser then finds Dark Fawful and fights him.
Dark Fawful is the second to last boss from Mario and Luigi Bowser's Inside Story. One of his attacks involves taking out a gun and shooting stars at Bowser. To avoid, Bowser must punch the largest star. Then Dark Fawful could have four plasma balls around him. Bowser must punch the Goomba provided to damage Dark Fawful. Dark Fawful can also pull out two holes and levitate over Bowser, tossing energy blasts into them. It depends on which hole Dark Fawful puts the plasma balls in to see if Bowser should Punch or use Shell Defense. Fawful can also use his headgear to grab onto the chandelier and swing into Bowser. The player must punch Fawful three times to send him flying, but be careful as Fawful will swing all the way around hitting Bowser as he does. His headgear can also spray a purple gas that can heal him.
- Dark Fawful resembles how Fawful looked at the end of Superstar Saga.
HP: 1736 and 2236 with Challenge Medal
Power: 334 and 834 with Challenge Medal
Defense: 184 and 684 with Challenge Medal
Speed: 48 and 548 with Challenge Medal