Kruller

Kruller is the third boss encountered in Luigi's Mansion 3. He is encountered and fought in the Lost and Found on the third floor. His name is a pun on "," a type of doughnut and a reference to the stereotype of police enjoying doughnuts. Defeating Kruller rewards Luigi with the elevator button to the second floor. It is possible to access the Mezzanine Kitchen prior to the fight with him, though Chef Soulfflé will not appear until after Luigi defeats Kruller to prevent sequence-breaking.

Appearance
Kruller is an overweight purple ghost in a dark blue security guard uniform with sunglasses, blue eyes and mouth, and short black hair hidden under a security cap.

History
Luigi briefly witnesses Kruller as the latter is doing his patrols on the third floor. After hearing noises, Kruller panics and tries to investigate the commotion, only to discover a mouse inside a flash vending machine. Dismissing it, he then enters his office, although he accidentally drops a key (the first key to a puzzle that results in getting the key to his office) when entering it.

Luigi can look into the office and can see Kruller reading a book while playing around with the elevator button.

When Luigi enters the office afterward, Kruller briefly faints from shock at Luigi entering, before entering the next room to find a suitable weapon to defend himself (humorously getting stuck on his back mid-roll), ultimately getting a water pistol.

Battle
Because Kruller is behind a barricade throughout his fight, the player has to fight him as Gooigi. Gooigi has to flash at Kruller and then suck in his glasses before flashing at him again to stun him. Kruller will also shoot squirts of water from his gun at Gooigi; if any of them hit him, he will dissolve, wasting time. In the final round, Kruller will make it more difficult to suck in his glasses. He can also charge his water pistol to shoot a long stream of water across the room. Upon being defeated, Kruller will struggle to avoid being sucked in to no avail. Gooigi then retrieves the Floor 2 button, with it being humorously revealed that Luigi slept through the entire battle (as Luigi is unconscious while Gooigi is conscious, and vice versa). After defeating Kruller in two-player mode, Luigi, who was watching the battle from outside, takes all the credit saying that he did it, after which Gooigi humorously copies Luigi as he had actually defeated Kruller.

Trivia

 * Kruller is one of the few bosses in a Mario game, besides tutorial bosses in the Paper Mario and Mario & Luigi series, where the player is unable to lose; they must fight him as Gooigi, and if Kruller hits Gooigi with his pistol's shots, Luigi can simply spawn him again.
 * Additionally, Kruller is the only boss ghost that is fought with Gooigi only.
 * Kruller and Chambrea are the only boss ghosts in Luigi's Mansion 3 that are scared of Luigi and unwilling to fight him.