Diva-Offs are face-offs between a number of "divas" for any number of reasons. They can be either impromptu or planned, and have been featured in all five seasons of Glee. They can be referred to as sing-offs, or mash-offs if the divas decide to sing a mash-up.
The first Diva-Off of Glee was planned after Kurt Hummel protested against the solo of Defying Gravity being given to Rachel Berry without an audition. After an official complaint from Kurt's father, Burt, Mr. Schuester decided to have a Diva-Off between Kurt and Rachel to decide who would be showcased. To decide the winner, both would sing the song separately for New Directions, the club members voting on who they believed sung the selection more skillfully. Ultimately, Kurt botched the High F purposefully in order to spare his father the homophobic attacks he would receive due to his son singing a song traditionally sung by a girl. Rachel was declared the winner, although Defying Gravity wasn't sung on screen again.
This impromptu Diva-Off occurred in the girls' bathroom. Rachel, hanging up audition flyers for New Directions to spawn interest, notices Sunshine Corazon and speaks to her patronizingly about joining Glee club as a background singer before continuing on with her flyers. Sunshine then begins singing Telephone and Rachel is horrified to find out she has an amazing voice. Threatened, she joins in, her opponent thinking the Diva-Off was only for fun. Their song is interrupted, however, by Sue who storms in and orders them to shut up, leaving the Diva-Off at a draw.
Sue, determined to destroy the Glee club from within, spreads lies to Mercedes and Rachel, telling each that the other had said slanderous things about her. The girls, angry with each other, declare a Diva-Off. Rachel lays down the ground rules that the song has to be from Broadway, giving her a home-field advantage. The two sing Take Me or Leave Me, both hostile before the song evolves into a tone of friendship. As the song ends, Mercedes and Rachel are hugging and laughing with each other, leaving Sue baffled.
Since the directors couldn't decide on who to cast for the role of Maria in their school-production of West Side Story, either Rachel or Mercedes, they decided to have a callback. Both sing Out Here On My Own within the scope of that, and the directors decide to double-cast the role of Maria. However, Mercedes resigns, leaving the role to Rachel.
Undetermined (possible draw as Santana got a confession from Sebastian, while he slushied her)
Pride Knowing what Sebastian put in the slushie
On a mission to discover what Sebastian had put in a slushie to cause Blaine to have surgery, Santana confronts him at Dalton. When she questions him he feels that she is questioning his honour and he challenges her to a duel.
They begin to perform Smooth Criminal with cellos backing them up. By the end Santana says to him "I was better." Sebastian replies with "not even close." She then demands for him to tell her what was then the slushie. He admits it was rock salt and it was meant for Kurt. He then slushies Santana.
After Jacob Ben Israel asks the question to the remaining New Direction members on who will be 'The New Rachel', too varying opinions. The inclusion of Unique pushes Blaine to announce that they will have a diva off after he declares that "Unique will be the new Rachel." As they meet Tina sets the rules that who ever sings Call Me Maybe the best, as decided by Artie, will be the lead vocalist. All four give their own spin to the song and as it continues on, the need to be the focus has them pushing each other to be seen. After a nearly a week to decide, and an inclusion of an online poll, Artie tells New Directions that Blaine won the title, Brittany being a close second.
Cassandra pushes Rachel in dance class yet again, believing she's a diva who's not ready for the opportunity she's been offered, but Rachel pushes back, insisting Cassandra's not appreciating how good she's gotten. The two face off in a dance showdown to All That Jazz from "Chicago": Rachel holds her own, but admits she's not the dancer Cassandra is; she's a better singer, however, and has a chance to win the contest with her voice.
NYADA Students (Adam, who voted for Kurt, among them), Brody (vote counter, voted for Rachel)
After Rachel won the NYADA winter-showcase in Swan Song, Rachel has become really full of herself. Kurt becomes so annoyed by that behavior that he challenges her to a diva-off. Rachel is sure she would win, since she won their diva-off in Wheels, but then Kurt reveals that he lost on purpose back then. Rachel is crushed, since it had raised her confidence a lot back then.
They then compete against each other at a public NYADA event. Due to Rachel's insufferable attitude, more people favored Kurt's performance, so he was announced the winner of the competition.
Rachel becomes discouraged by her loss, and doesn't want to audition for an upcoming musical any more, thinking that she will become too bigheaded if she becomes successful. She needs to be build up by Kurt again after that.
The performance goes on with the two singing and exchanging challenging looks. They stand in front of Marley as they sing, trying to impress her by pushing and shoving each other to be in front. Ryder and Jake then throw their hats away. As the duet progresses, the boys even dare to throw their glasses onto the floor as the Glee Club watches the intense duet duel. They jump onto one of the cupboards and rip off their suits and pants, like Superman would, revealing their superhero costumes. Both have the initials "MS" for MegaStud. The song ends with a quarrel and Jake and Ryder end up punching each other and literally fighting for Marley and Finn pulling them apart.
Artie and Tina, who have been at odds due to valedictorian, intensify their competitive feud, both nominating themselves and competing against each other for the second solo at Nationals. The other New Directions provide backup while they sing, and during the song, the two stand by their previously-established opinions, Artie claiming Tina has changed for worse between their junior and senior year, and Tina claiming that Kitty doesn't really love Artie and is just using him. Although it starts well, the song is sharply interrupted when Tina accidentally pushes Artie off his wheelchair, which leads him to leave the Choir Room angry.
Rachel and Santana continue their feud in the workplace. When a customer requests a song for his daughter, both volunteer to perform it in order to win over Elliott. They fight throughout the performance, taking each other's lines and pushing each other around the restaurant.
While being interviewed on Fondue For Two, Rachel and Mercedes realize that they plan to sing the same song to glee club. Continuing their feud, both are adamant that it is 'their' song, and so Rachel suggests a "good, old fashioned diva-off" to settle the score. Mercedes happily agrees.
Annual Boys vs. Girls Mash-Offs
Every year (and Season) a Mash-Off between the New Directions Boys and the New Directions Girls. A mash-off is a kind of diva-off where both teams are required to sing a mashup. In Season Three, the off was between New Directions and The Troubletones, but it can be considered am equivalent since the Troubletones held three then former New Directions Girls. and New Directions only had Tina and Quinn because Rachel had been suspended. Up to now, there has never been a winner of these mash-offs.
This mash-off was held as a competition to heat up the Glee Club because they had been lazy after knowing their competition for Sectionals wasn't very hard to beat. The incentive of the competition would be having power of decision over the showstopping number at Sectionals. But there was trouble when both teams went to the then school nurse Terri for help and they were given vitamins to improve their performances (first to the boys and then the girls). They would have probably had a draw, but Rachel and Finn decided to tell Mr. Schue the truth, having both teams disqualified and Terri fired.
This mash-off wasn't held as a competitive off. The assignment (apart from singing a mashup) was the girls had to sing music the boys liked and vice versa. Since this off wasn't competitive, there wasn't a winner.
This is a Glee club mash-off Will (coach of New Directions) and Shelby (coach of The Troubletones) put together as a way of sane competition between Glee Club, but Santana and Finn get a lot more competitive. It is unknown if a winner has been chosen and, if there has, who it was.
This is the only mash-off not held in the Season's sixth episode, but in the fifteenth. The theme was movie songs and it was held to see which team would star in Artie's future movie. The winner is declared to be everyone (much to the Glee Club's dissent) because Artie needed a lot of fresh faces in his upcoming project.
The character that has taken part in the most Diva-Offs is Rachel.
The most recurring rivalries are Rachel vs. Kurt and Rachel vs. Mercedes (2 Diva-Offs were held for each).
Ironically, the three of them have a Diva-off in 100.
Kurt is the only characters to have ever officially beaten Rachel in a Diva-Off.
Season Two and Season Four had their first Diva-off in their first episode (Rachel vs. Sunshine in Audition and The New Rachel-Off in The New Rachel), which is the earliest a season had its first off.
All of the Boys vs. Girls Mash-Offs were judged by Will and a Special Guest Judge.