More on Katy Perry later, but first the music and the competition.
This episode featured the genre group where contestants chose their favorite genre in which to compete. Those who advance will get to compete in the next round: Hollywood Duets.
Three contestants got to sit out this round. Huntergirl, Jay Copeland, and Kenedi Anderson earned so-called Platinum tickets during their auditions.
The first mentor of the night was Lauren Alaina, runner-up on the 10th season of Idol. She advised of the country genre group, which was pretty big.
The first time Kelsie Dolin performed in front of anyone besides her family was her American Idol audition.
Her appearance in Hollywood would be her first chance to perform on stage.
"I know it is overwhelming. However, this show was created for Kelsie," Alaina told her. "You are what American Idol is all about. This is your moment."
She was visibly shaking on stage and appeared to be frozen until the music started, and then Kelsie owned the moment.
Kelsie sang "Things a Man Oughta Know" by Lainey Wilson.
Contestant Mike Parker says he is doing it for his mama who was diagnosed with leukemia during his audition. He sang 'Burning House' by Cam.
"I was thinking about my mom the entire time," he said after the performance.
Kaylin Roberson from North Carolina sang "Crazy" while construction worker Noah Thompson, who signed up for the competition thanks to his best friend, also sang "Burning House."
The second genre of the night was R&B and brought back season 2 winner Ruben Studdard to mentor the contestants.
Tobias ignored Ruben's advice to ease up on his runs during his performance of "Back to One."
Lionel Richie said he should have taken "half out of it" but Tobias still advanced to the next round.
Baltimore's Katyrah Love told us before her performance that she serves a population of youth who are homeless.
"I want to show my community if you put in the hard work and the effort and have a little bit of hope, anything can happen for you," she said.
Katyrah gave a simple but strong performance of Whitney Houston's "Saving All My Love."
2010 Idol Lee DeWyze joined the show to mentor the Indie-Folk genre and a group of self-described "oddballs."
Leah Marlene from Normal, Illinois took the stage first with her quirky energy.
She chose "Sk8er Boi" by Avril Lavigne for her performance. Leah said she wanted to stick in the judges' brains.
"Don't be afraid to explore that chorus. Your voice is unique. Be who you want to be," DeWyze advised. "Be who you are."
Fritz Hager got a no from Luke Bryan during his audition, but he is determined to advance. Fritz attempted an acoustic version of "Unsteady" for his Hollywood song.
Katy Perry called his performance a "big surprise."
Both Leah and Fritz advanced to the Hollywood duets!
The next guest mentor in the soul genre was Haley Reinhart, a third-place finalist in season 10.
Tristen Gressett needed to tone things down from his audition and he took the advice to heart to the delight of the judges.
Danielle Finn is 17 with a remarkable range. She earned a standing ovation with her performance of Adele's "Easy On Me."
Christian Guardino from Long Island said he was very shaky and nervous during his Nashville audition, and he wanted to turn that around.
He performed "My Future" by now Oscar winner Billie Eilish.
Season 7 winner David Cook returned to mentor the rock genre group.
Cole Hallman from Manasquan, New Jersey is relatively new to the stage and seemed a bit green for his Hollywood song, Billy Joel's "Vienna."
"We're going to keep rolling the dice on you, but you will not be able to get through on dice rolls much longer" Luke Bryan warned him.
The pop genre group is crowded and young.
2007 American Idol winner Jordin Sparks gave some advice to Chicago's Sir Blake that appeared to help as he took to the stage to perform "True Colors."
"Much better than his audition," Katy Perry said.
Ava Maybee's dad is Chad Smith from the Red Hot Chilli Peppers, but she is looking to make it on her own merits. She performed "Roxanne" in a unique style.
Emyrson Flora is used to singing into her phone in her bedroom, but she is crushing it on stage too.
Jacob Moran is taking a second shot at becoming an Idol. He did not make it through Hollywood last time out, and he had a tough time in this round.
Nicolina Bozzo wants to show her sisters that dreams can come true. She closed out the genre with a cover of Billie Eilish's "Everything I wanted."
Other moments from the show included last year's winner Chayce Beckham returning to coach the contestants on how to use the judge's advice to get better.
And Katy Perry had a wardrobe malfunction during a performance of her hit song "Teenage Dream." She was singing along with her fellow judges, bent down, and ripped the back of her red, leather pants!
The Platinum Ticket winners Huntergirl, Jay, and Kenedi, who had been watching all the performances, sang Journey's "Don't Stop Believin" to close the show.
As a bonus to sitting out this round, they will get to CHOOSE their duet partner. The judges will assign all of the other contestants.
Watch the next American Idol on Sunday at 8 p.m. ET/PT | 7 p.m. CT on your local ABC station and the next day on Hulu.