It wouldn't be Hollywood if celebrities didn't push the boundaries or go over the top with their Halloween costumes year after year. 

From barely-there attire to pop-culture references galore, the biggest stars showed up and showed out for the spookiest day — or weekend — of the year.

MEGAN FOX AND MACHINE GUN KELLY CRUCIFIED FOR 'MOCKING' CHRISTIANITY IN HALLOWEEN COSTUMES: 'ABHORRENT'

Most Controversial

Kendall Jenner

Kendall Jenner went as Jessie from "Toy Story"

Kendall Jenner dressed up as Jessie from "Toy Story." (Instagram)

Kendall Jenner angered some fans with her Jessie costume from "Toy Story" this Halloween. Posing in a more scantily-clad outfit than the original animated Pixar character, some on Instagram were critical of Jenner, with one person writing, "You're just sexualizing a child's character."

While Hollywood friends like model Lily Aldridge and singer Normani were complimentary of her take on the cowgirl, others were not as amused, with one person writing, "childhood = ruined."

Kim Kardashian

Kim Kardashian as Mystique for Halloween

Kim Kardashian's makeup as Mystique from the "X-Men" series was spot-on. (Instagram)

Jenner's big sister Kim Kardashian had the ultimate Halloween faux-pas: showing up to an event that was not, in fact, a costume party. Although her makeup as Mystique from Marvel's "X-Men" was superb, the reality star took to her Instagram stories to share an embarrassing tidbit about her Halloween weekend.

"That time I showed up to a birthday dinner in full costume when it wasn't a costume party," she wrote beneath a picture of her as Mystique alongside birthday girl Tracee Ellis Ross.

Kim Kardashian and Tracee Ellis Ross

Kim Kardashian showed up to Tracee Ellis Ross' birthday dinner decked out in her Halloween costume. (Instagram)

Megan Fox and Machine Gun Kelly

Megan Fox and Machine Gun Kelly ruffled feathers not once but twice for their Halloween costumes this weekend. 

On Friday, Fox and Kelly went to the annual Casamigos Halloween party as Tommy Lee and Pamela Anderson, which angered some people given the abusive nature of their relationship.

Megan Fox and Machine Gun Kelly communion Instagram

Megan Fox and Machine Gun Kelly faced serious backlash for their Halloween costume. Many Christians were offended by the rappers choice to be a Priest and given Fox communion. (Instagram)

On Sunday, Fox captioned a photo of her and Kelly "On Sundays we take communion." Users on social media were quick to condemn Fox for the religious theme of her costume, where she appeared to be receiving communion from Kelly, who donned a Priest costume.

One person commented, "So disrespectful. Absolutely disgraceful and offensive."

Most Ruthless

Frankie Jonas and Anna Olson

Frankie Jonas and girlfriend Anna as Joe and Taylor Swift

Frankie Jonas dressed up as his big brother Joe Jonas, while his girlfriend Anna Olson went as his famous ex, Taylor Swift. (Instagaram)

He might be known as the ‘Bonus Jonas,’ but Franklin "Frankie" Jonas and his girlfriend Anna definitively won the best-dressed Jonas, going as Joe Jonas and his ex-girlfriend Taylor Swift, in a hilarious spoof. 

Frankie and his girlfriend mocked the short-lived relationship between Jonas and Swift, writing in his caption "#jonasbrothers3dmovie #streammidnights" in reference to the 3D concert movie of his elder brothers and musical group The Jonas Brothers, as well as Swift's new album "Midnights."

In another photo, Frankie mocked his big brother's choice to wear a purity ring throughout his teenage years, a decision that was wildly taboo to discuss at the time.

Josh Duhamel and Audra Mari

Josh Duhamel and his wife Audra Mari

Josh Duhamel and his wife Audra Mari poked fun at their 21-year age gap. (Alberto E. Rodriguez/WireImage)

Keeping with the theme of being in-on the joke, Josh Duhamel, 49 and his wife Audra Mari, 28 poked fun at their 21-year age gap by dressing up as billionaire J. Howard Marshall and his young wife, the late Anna Nicole Smith. 

The two famously had a 63-year age difference. In the photos, Duhamel is seen with a walker, being led into the party by Mari.

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Best Couples/Group

Elle Fanning and Max Minghella

The rekindled duo of Elle Fanning and Max Minghella went the spooky route for their couples Halloween costume this weekend, going as Tiffany Valentine and Chucky from the scary movie "Child's Play."

Elle fanning and Max Minghella

Elle Fanning went as Tiffany and Chucky from the horror flick "Child's Play." (Instagram)

The actress posted to her Instagram the famous quote from the film, "Wanna play?" along with a series of photos of the two posing. Minghella wore a mask, while Fanning transformed herself into character through makeup.

Ariana Grande and Liz Gillies

Ariana Grande and Liz Gillies Halloween

Ariana Grande and Liz Gillies earned tremendous praise for not only their Halloween costumes, but also scene re-creations of Jennifer Coolidge and Jane Lynch's characters in "Best in Show." (Instagram)

Ariana Grande and her "Victorious" co-star Liz Gillies went the extra mile for their costumes as Sherri and Christy, characters portrayed by Jennifer Coolidge and Jane Lynch respectfully in the film "Best In Show."

Not only did the women nail the costumes, but they also recreated scenes from the movie. Coolidge commented on the Instagram post, writing, "This is f***ing great."

Several other celebrities commented, including Katy Perry who wrote "can this get nominated," while Victoria Justice wrote "this is amazing."

Lili Reinhart, Camila Mendes, and Madelaine Petsch

"Riverdale's" famous trio, Lili Reinhart, Camila Mendes, and Madelain Petsch nailed their portrayal of the Sanderson Sisters from "Hocus Pocus" this Halloween. 

The girls of "Riverdale" went as the Sanderson sisters from "Hocus Pocus"

The three lead women in the CW's "Riverdale" Lili Reinhart, Camila Mendes, and Madelaine Petsch perfectly embodied the Sanderson Sisters from "Hocus Pocus." (Instagram)

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The three women, who happen to have blonde, red, and brown locks just like the characters from the Disney movie, posed like the characters portrayed by Sarah Jessica Parker, Bette Middler, and Kathy Najimy.