Half of the 32 "X Factor" semifinalists performed on Thursday's (October 13) episode, which was delayed by a day due to Fox's coverage of Major League Baseball. The contestants ventured off to their mentors' luxurious homes and strutted their stuff in front of them, each vying for one of 16 spots in the finals.

In three out of four cases, the judges were joined by a super-special celebrity guest: In Santa Barbara, California, Paula Abdul was accompanied by Pharrell Williams; Enrique Iglesias was coupled with Nicole Scherzinger in Malibu, California; and Rihanna was by L.A. Reid's side at his cozy estate in the Hamptons, New York. Meanwhile, over in France, Simon Cowell was stood up by Mariah Carey, whose plane was grounded by Hurricane Irene. When it was time to make decisions, a vocal coach and a team of music producers were there to give their impressions to Cowell, whose backyard, it should be noted, houses an absolutely enormous swimming pool.

Simon's pool aside, it was Rihanna who was the episode's MVP. Not only did she help provide Reid feedback on the contestants, but three of them performed her songs, including Seattle crooner Phillip Lomax, who took RiRi by surprise with his laid-back, Sinatra-style take on "Don't Stop the Music." Other singers taking on Rihanna songs were Temecula, California, Bieber-hair-sporting brother duo the Brewer Boys, who did a Tejano version of "Only Girl in the World," and James Kenney, who took on the emotionally charged "Russian Roulette."

As a judge, RiRi seemed most taken by pint-size 14-year-old rapper Brian "Astro" Bradley, whom she compared to "a mini J. Cole." And the brimming-with-confidence Bradley didn't hesitate to inform RiRi of his future plans with her, telling her frankly, "We will be doing a collab one day."

The Carey-less Cowell is tasked with mentoring the girls in the competition, and the standouts included 14-year-old Drew Ryniewicz, whose slowed, hushed take on Roxette's "It Must Have Been Love" was called "magic" by the tight-T-shirted one, and rugby bruiser Caitlyn Koch, whose "Will You Love Me Tomorrow" caused Cowell to praise her pitch and tone. Cowell also enjoyed Simone Battle's piano-ballad version of the Beatles' "Help," but he seemed less sure about Tora Woloshin's electro version of "(I Can't Get No) Satisfaction": "It doesn't quite get to me," a puzzled Cowell explained.

In the groups category, Salt Lake City, Utah, trio the Anser impressed Paula and Pharrell with their version of Pink's "Perfect," though Pharrell seemed perplexed by a group member's decision to leave his striking red-framed glasses off during the performance. Virginia Beach quartet 4Shore were praised for their sound take on Brownstone's "If You Love Me," though Pharrell suggested the group needs to "dirty up their style a little bit." And both the judges and the members of Lakoda Rayne seemed to agree something was "off" during their performance of Lady Gaga's "Born This Way," not surprising, considering the group was Frankenstein'd together by the judges and had never previously performed together as a unit.

In the category of the Olds — sorry, the "Over 30s" — 53-year-old Elaine Gibbs and 42-year-old Stacy Francis stood out with their versions of Oasis' "Stop Crying Your Heart Out" and Prince's "Purple Rain," respectively. (Of the latter's, which seemingly echoed throughout the canyons of Malibu, Iglesias marveled, "I think the neighbors heard that.") But the most memorable performance (for all the wrong reasons) came from formerly homeless 49-year-old Dexter Haygood, who strutted like Mick Jagger and kicked his legs in the air like David Lee Roth while screaming his way through Beyoncé's "Crazy in Love." Iglesias practically buried his head in his hands in horror during the performance, and many viewers probably did too.

On Sunday's "X Factor," the second half of the contestants performs in front of the judges, and the talent pool is cut in half from 32 to 16.

Who should make the "X Factor" finals and who shouldn't? Let us know in the comments!