Halloween 2021 is officially in the books, and the stars certainly took advantage of having a year off from celebrating, putting a ton of effort in for this year's bashes.
Megan Thee Stallion -- dressed as a fairy -- hosted a huge event at Ysabel in West Hollywood ... one of the more notable costumes from that party was Adam Lambert, who was all decked out as some sort of aquatic king.
The Weeknd went all out for his costume, per usual, as Don Vito Corleone from "The Godfather" with full prosthetics ... he really looked like the real deal.
Doja Cat, dressed as Cynthia from Rugrats, Anderson .Paak pulled off the perfect Bruno Mars and Anastasia 'Stassie' Karanikolaou dressed as "Joker" for Kendall Jenner's private birthday party at Harriet's Rooftop in West Hollywood.
Preaching public health,Katy Perry and Orlando Bloom dressed as a doctor and vaccine titled "Katy & Perry" ... perhaps a play on Johnson & Johnson.
As for couple's costumes, Travis Barker and Kourtney Kardashian paid tribute to the movie "True Romance" with their Halloween look ... and Kylie and Travis Scott took Stormi trick or treating.