Actor Mario Lopez was Tony Manero from "Saturday Night Fever."
Actress Hillary Duff and her boyfriend Jason Walsh were criticized for dressing up as a Native American and a Pilgrim.
The costume was viewed as an insensitive appropriation of Native American culture. Both Duff and Walsh have already apologized for the choice.
Actor Kelsey Grammer portrayed Sideshow Bob, a character from "The Simpsons."
Bette Midler recreated the costume of Winnie Sanderson, her character in "Hocus Pocus."
Actress Jenna Dewan was a unicorn.
Model Cindy Crawford and her family dressed as punks.
Crawford's daughter and son have already launched their own careers in the fashion world.
"Family Guy" creator Seth MacFarlane went as Oscar the Grouch.
Comedian Kathy Griffin used makeup to recreate a popular Snapchat filter.
Famous feminist Gloria Steinem (pictured here with actor Alan Alda) was Medusa.
Late night host James Corden (pictured here with his wife Julia Carey) was a NASA astronaut.
Actor Zach Braff channeled Tom Cruise's Maverick from "Top Gun."
Swimmer Ryan Lochte went all out on his Mad Hatter costume.
And actor Taylor Lautner dressed up as Ryan Lochte.
Turns out Lochte was a popular costume this year: Actress Nina Dobrev portrayed him, too.
Dobrev and her friend also emulated a grisly scene from "The Revenant" in which Leonardo DiCaprio's character stays warm inside a sliced-open horse.
Actor Matthew Morrison and his wife, Renee, went as the Joker and Harley Quinn.
Kylie Jenner looked just like Christina Aguilera in the 2002 music video for "Dirrrty."
Kourtney Kardashian and a friend went as a zombie-esque bride and groom.
Beyoncé recreated the look from Salt-N-Pepa's video for "Push It."
Singer Katy Perry used prosthetics to transform into Hillary Clinton.
Actress Elizabeth Banks (right) was Mia Wallace from "Pulp Fiction."
Actor Jacob Tremblay somehow became even cuter when dressed as Marty McFly from "Back to the Future."
Singer Mariah Carey opted for a classic devil outfit.
Actress Mindy Kaling made a hilarious Sully Sullenberger.
Singers Demi Lovato and Nick Jonas were Dorothy and the Scarecrow from "The Wizard of Oz."
Comedian Amy Schumer and her boyfriend were the characters Dustin and Eleven from the hit TV series "Stranger Things."
Martha Stewart had two costumes up her sleeve: First, a bloodied nurse ...
... and second, Marilyn Monroe.
Nicole Richie and a few friends stepped out as magicians Siegfried and Roy (complete with a tiger).
Paris Hilton was inspired by Alice in Wonderland.
Actress Vanessa Hudgens went as a fortune teller.
Actress Sarah Hyland described her look as "fairy queen of the swamp."
Actor Colton Haynes seriously committed to this Miss Piggy costume.
