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When We Were Young music festival attendees thought they knew what they were in for on Saturday.

Iconic emo/pop-punk songs like Blink-182's "All the Small Things," Green Day's "Boulevard of Broken Dreams," Yellowcard's "Ocean Avenue," and Good Charlotte's "Lifestyles of the Rich & Famous" could be heard during every single set as artists played their biggest and most enduring hits for dedicated fans braving the 91 degree Las Vegas heat on the first day of 2023's massive event. But some bands veered from their expected set lists to include some surprising song choices that no one saw coming — and they all rocked.

Below, EW rounds up the best covers performed during When We Were Young, from Frozen to "Iron Man" and more.

Remember all those fan-favorite Punk Goes Pop albums? New Found Glory love delivering something more like Punk Goes Movies, as evidenced during their early Saturday set by dropping a heavy cover of "Let It Go" from Frozen ... and it's just so random that it works. Lead singer Jordan Pundik's attempts to hit notes not even Idina Menzel could dream of were an added bonus as people moshed their way through a Disney ballad.

In between delivering hit after hit in their short set, Simple Plan still found time to delight fans with a three-song medley of covers — each one better than the last. Singer Pierre Bouvier first led the Canadian band through a harder version of Avril Lavigne's "Sk8er Boi" hours after she dropped in for a surprise appearance during All Time Low's set to perform that same song. Then the band continued with a high-energy cover of Smash Mouth's "All Star" before concluding the medley with the Killers' "Mr. Brightside." As if that wasn't enough, they also performed their theme song for the animated series What's New, Scooby-Doo? as people in Scooby-Doo costumes ran around dancing on stage. With the fan response to the performance as well as the size of the crowd, it's clear Simple Plan should have been on the main stage rather than a smaller side stage.

The reason All Time Low covered George Michael's hit "Careless Whisper" is pretty simple: "Why? Because, why not?" lead singer Alex Gaskarth told EW. While the band performed this cover during Friday night's official When We Were Young side show and not during their set on Saturday, it absolutely still counts because it was so unexpected and smooth. Gaskarth may have been reading the lyrics on his phone but Andrew Kyne, the saxophone player from opening band Grayscale, crushed the melody so well (and often) that George Michael would be proud.

Headliner Green Day were busy long before the festival began. Two days before their planned closing set on Saturday, the band performed their classic 1994 album Dookie in full during an intimate secret pop-up concert on Thursday. They also debuted a new track, "The American Dream Is Killing Me," which Armstrong called "the first song off our new album," and they announced a stadium tour in 2024. Meanwhile, their festival set leaned more into their 2004 album American Idiot, but frontman Billie Joe Armstrong snuck in a snippet of Black Sabbath's instantly recognizable "Iron Man" during "Hitchin' A Ride."

Sum 41 has an extensive list of anthems on their own discography, but they added another from a different band during their set when they performed their classic cover of Queen's "We Will Rock You." The crowd clapped and stomped along to the iconic beat as singer/guitarist Deryck Whibley belted the lyrics.

Watch videos of some of the best covers from the day below:

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