Shadow Bowser

Shadow Bowser is the apparition of the fourth mansion and is a darker version of Bowser. He just like Bowser in every way except his attacks are 10 times more lethal than that of the original. After the third hit, Shadow Bowser attempts to wipe out Luigi with a single blast of pure dark energy, but Luigi avoids this by taking cover behind Shadow Bowser, which is the only safe place from the attack and Shadow Bowser's only weak spot. After being sucked up, Luigi receives the key to the Haunted Aquarium and the Shadow Claw, which lets Luigi play the minigame "Shadow Bowser Returns".