Polterkitty is Hellen Gravely's beloved ghostly cat which appears as a recurring boss in Luigi's Mansion 3. Her behavior is similar to that of Polterpup in Luigi's Mansion: Dark Moon, though compared to Polterpup she is more malicious.
Polterkitty is first seen in a cutscene after Luigi rescues Toad, sitting on Hellen Gravely's lap while she watches Luigi's progress. After Luigi retrieves the 9F elevator button from Morty in Paranormal Productions, Polterkitty steals and eats the button as soon as it is placed in the elevator. Luigi must find Polterkitty by using his Dark-Light Device to reveal her trail: invisible footprints where she's walked and silhouettes where she's phased through walls. Eventually, Polterkitty will be flushed out and left vulnerable to a flash from Luigi's Strobulb, provoking her to seal off the room as she transforms into a large, panther-like monster. Luigi must face away from Polterkitty's perch to make her drop down for a sneak attack; if he turns around too soon, she'll immediately return to her perch and wait for him to turn his back again.
To defeat Polterkitty, Luigi or Gooigi needs to flash the Strobulb at her just before she attacks, indicated by her rearing up and spreading her forelimbs wide as her eyes flash pink. This will stun her long enough for Luigi or Gooigi to catch her with the Poltergust G-00. Polterkitty does not take damage from the suction; instead, she must be repeatedly slammed into the ground like a Gem Goob. When her HP is reduced to 1, Polterkitty loses one of her tails to the Poltergust G-00, allowing her to flee to the Garden Suites. Luigi must follow her and repeat the process of flushing her out and provoking her attacks to remove her other two tails; when she loses her last tail, Polterkitty spits up the 9F elevator button and retreats.
Polterkitty reappears after Luigi retrieves the 14F elevator button from Johnny Deepend in the Fitness Center, once again stealing the button after it is placed in the elevator. This time, Polterpup helps Luigi track down Polterkitty, and together they hunt her down in the same way as before. Polterkitty has regrown the tails she had lost previously and increased her HP to 100. She flees to The Spectral Catch after losing one tail, then moves to the Twisted Suites when she loses the second. When Polterkitty is cornered for the third and final time, she attempts a fake-out of her own; as soon as Luigi turns to counter her attack, she quickly goes right behind him to attempt another slash attack. If Luigi reacts to this in time to stun Polterkitty, he will have a chance to completely suck her into the Poltergust G-00, retrieving the stolen elevator button and ending her mischief for good.
Upon confronting Hellen Gravely in the Master Suite, she specifically mentions Polterkitty's capture as one of her many grievances against Luigi prior to their battle.
In the Gallery, Polterkitty shares the same containment jar as Hellen Gravely, although she will not appear until the latter is captured.
In the credits, she can be seen along with Hellen Gravely.
Polterkitty acts like a normal cat in a sense; playing with random objects and easily frightened. She, like Polterpup, is mischievous but with more malicious intentions. She is poised, elegant, and calm as evidenced when she struts out of the elevator after taking the button. Polterkitty appears to be rather stuck-up as she snubs the playful Polterpup in his attempts to befriend her. Polterkitty is the only being Hellen cares about, aside from King Boo; as such, she has undivided loyalty to her, doing what she can to help her on her quest to defeat Luigi. Similar to Hellen, Polterkitty has sadistic tendencies as she lays out several traps for Luigi as he tracks her down, even smiling when she summons several ghosts to attack him and Polterpup in the Fitness Center. In her beast form, Polterkitty is much more feral and deadly, stalking Luigi when his back is turned to strike. She displays a more cowardly nature when Luigi turns to look at her, as she covers herself in fear.
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