The pressure was turned all the way up on Wednesday night's the "X Factor." The episode kicked off with the finale of the boot-camp round, during which the contestants learned their fate, before only 24 headed off to the judges' houses to get some one-on-one attention. A lot was on the line for the show's hopefuls, and in the end, only a few could survive.

Boot Camp Wraps Up
With their time in Miami nearly over, Simon Cowell reflected on the experience. "We've put them through a lot, it's the moment of truth," he shared ahead of the bloodletting. After more than half the singers were told they wouldn't be advancing, the singers then learned they'd be competing in groups of Teens, Young Adults, Over 25s and Groups.

CeCe Frey, Willie Jones, Janelle Garcia, Nick Youngerman, Paige Thomas and Jillian Jensen all had been plucked to compete in the Young Adults group. Meanwhile, Jason Brock, Daryl Black, David Correy, Tara Simon, Tate Stevens and Vino Alan nabbed spots in the Over 25s group.

The Groups included spots for Sister C, Dope Crisis and Emblem3. The judges also formed three additional super groups from remaining contestants: Lylas, Lyric 145 and Playback. The Teens group included Beatrice Miller, James Tanner, Carly Rose Sonenclar, Diamond White, Reed Deming and Arin Ray. As the eliminated contestants walked out, Demi reflected, "I remember being one of those girls."

Fates Are Decided
After boot camp wrapped up, the judges learned what teams they'd be heading up. Britney Spears got the Teens. "Are you serious? Oh my god! That is amazing," she declared upon learning she got the team she wanted. Simon will mentor the Groups. "I'll make the most of it. I'm happy for them." (He's had "X Factor" group success with One Direction, FYI.)

Demi Lovato happily learned she'd be leading the Young Adults. "I have the winning team," she promised. L.A. Reid was very much unhappy to learn he had been gifted with the Over 25s. "The what?" he angrily said, before slamming the phone down and later storming off.

The Mentors
Things got a bit cheerier when the groups met their respective judges and their hand-picked mentors. Marc Anthony chilled with Simon in Miami and will.i.am joined Britney in L.A.

Nick Jonas, as he promised MTV News earlier, took the gig seriously, telling the Young Adults, "I'm here today to get you to be the best you can be."

Ironically, the youngest mentor, Justin Bieber (with manager Scooter Braun by his side) had some words of wisdom for the oldest set of competitors, the Over 25s. "They told me I was too young and you're never too old or too young," he advised. "You definitely are in good hands," he added of L.A.

Up Close and Personal
Viewers got the chance to see two of the groups perform. And while six from each group went in, only four would walk out. (Their fates would be decided in a later episode.)

In the Young Adults group, Demi and Nick doled out advice to the pretty young things, which the competitors took in stride. Garcia tried her hand at Katy Perry's "I Kissed a Girl." Jones wanted to redeem himself by performing "Nobody Knows" by the Tony Rich Project. "I do think there's a place for him, but he's going to need to find that," Nick said of his constant switching of genres from R&B to country.

Jensen went for Sara Bareilles' "Gravity" which made Nick very, very happy. "Maybe it's outta line, but shes kind of sexy, it's the voice tied with the passion," he said. Youngerman sang a gender-bending twist on "Tik Tok" by Ke$ha. "I couldn't tell if I was loving it or if I was super annoyed by it," Demi noted.

Rihanna look-alike Thomas tried her hand at a slowed down version of Chris Brown's "Turn Up The Music." Her performance left Demi feeling uneasy. "This just got very confusing for me," she said, noting that she hasn't been dazzled by her since that first performance at her audition.

Meanwhile Paige's archrival, Frey got a warning that she comes off as unlikable from Demi before she performed. She tried to show she was vulnerable by singing LMFAO's "Sexy and I Know It." Despite that mixed message, Nick noted that "she took direction extremely well."

The groups had their shots next. "This could be the first day of the rest of your life, or not," Marc warned.

Newly formed Playback put a hip-hop spin on Hall and Oates' "Rich Girl." Simon was into it, Marc wasn't. Marc did give Emblem3 his seal of approval with their rap/sung version of the Police's classic, tune "Every Little Thing She Does Is Magic."

Texas sisters, Sister C, were told they come off as "standoffish" so they tried to warm it up with their version of Shelby Lynne's "Leavin'." "They are contenders for the real world," Simon said.

Lyric 145, comprised with Lyric Da Queen and One4Five, was formed at auditions and the hip-hop trio decided that the best way to show off they deserved to still be in the competition was with their booming version of Miley Cyrus' "Party in the USA." The term "superstar" was thrown around after they walked off the stage.

Dope Crisis went for Nicki Minaj's "Super Bass," where they flipped the gender on the track. And, finally, Lylas, which was another group formed at boot camp, went for "Impossible" by Shontelle. The final performance of the night was described as "unbelievable" by both judges.

What was your favorite performance on Wednesday night's "X Factor"? Leave your comment below!