Massive Multiplayer Ensemble Number

A common trope in musical theater, a song (often one that ends the first act) that sums up the attitudes of all of the main characters toward some upcoming event or towards something that happened earlier by having them singing all at once, with counterpoint for all.

Frequently overlaps with The Song Before the Storm, which refers to any large-scale songs about an upcoming confrontation.

Film

 * "At the Opera Tonight" from Repo! The Genetic Opera: Shilo sets out for the opera house, Mag resigns herself to her fate, Nathan puts on his Repo Man gear, Amber Sweet buys one last round of Zydrate from Graverobber, Rotti Largo plans the outcome of his final masterstroke, Pavi Largo rejoices over his new face and the possibility of getting laid, and Luigi Largo is... angry, because he's Luigi Largo. This song has even been described as "'One Day More' with electric guitars".
 * High School Musical does this a lot.
 * Not Another Teen Movie has one right before the Prom scene, where each main character talks about their current feelings, along with a random chef who announces he's just jerked off in someone's french toast.
 * Disaster Movie has "Date Song", which brings together many of the movie's characters, even ones that have been killed during the movie, to sing a curtain call song... then it's Drop the Cow time! (This is the unrated version -- the PG-13 version replaces the word "fuck" with "date", hence the song's title.)
 * "La Resistance" from the South Park movie.

Live-Action TV

 * "Walk Through the Fire" from the musical episode of Buffy the Vampire Slayer.
 * And "Where Do We Go From Here".

Theatre

 * The definitive example is the "Tonight" ensemble from West Side Story, which directly precedes the first act's violent final scene.
 * "Ever After" from Stephen Sondheim's Into the Woods, which actually serves as what seems like an ending to the whole show by showing the happy endings reached by the fairy-tale characters seen in the first act--until The Narrator says "To Be Continued!"
 * More appropriately the opening number "Into the Woods" and the act two opener "So Happy" fit this trope better.
 * From Sondheim's Sweeney Todd: The Demon Barber of Fleet Street, "God That's Good!" and "Johanna (reprise)".
 * "A Weekend in the Country" from A Little Night Music.
 * "It's Hot Up Here" and "Putting It Together" from ''Sunday in the Park With George."
 * Sondheim really likes this trope.
 * Three songs from the Andrew Lloyd Webber musical Starlight Express did this: First, there was the opening of Act II, in which all the engines prepared for the big final race in the championship. In the West End production and the recent US tour, it was called "The Rap," and was rewritten three times, basically because the first one didn't really sound like rap. The second one, written in 1992, sounded a little more like rap, but the early period. In 2003, a new rap was written which more accurately represented the genre. For the 1987-1989 Broadway version exclusively, a new song was added as kind of a continuation to the "Freight" coda, which had electricity, steam, and diesel fighting against each other in contrapuntal song, which then led to the big races which would then end with one train winning the "Silver Dollar" (rather than the Champion of the World). The other song that falls in this category is "The Hymn To Victory" which has been in every production since. This is another continuation of the aforementioned "Freight" Coda, with everyone raising their voices in an even louder, earth-shaking chorale, with a massive High C from Rusty. Here, this song is sung before the final heat, specially prepared on a downhill course. Rusty joined in the singing, even though he was disqualified from the final, so you can hear the Control's voice ordering for the Marshals to stop Rusty from entering the tracks,
 * "One Day More" from Les Misérables, which reprises virtually all of the songs in the show up to that point in the story and has all of the main characters planning for the coming insurrection--Jean Valjean plans to take his adopted daughter Cosette away from France to keep them from being discovered, Cosette and her boyfriend Marius despair of ever seeing each other again, Marius takes Cosette's leaving as a final sign that he needs to join the students on the barricade, Eponine pines for Marius, Enjolras and the students look forward to taking on The Man, Javert announces his plan to spy on the students, and the Thenardiers look forward to rich pickings from the bodies of the dead, all in one four-minute musical number.
 * This was the direct inspiration for the Act I finale of Urinetown.
 * And for "When the Truth Comes Out" from the Musical Episode of Scrubs.
 * And, most recently, from the creators of "La Resistance" and "When the Truth Comes Out," the act one finale to The Book of Mormon called "Time Ta Man Up". It starts out like an '80s rock parody a la "Montage" from Team America, but then once the rest of the cast comes in, it turns into a MMEN.
 * "Prima Donna" from The Phantom of the Opera is a non-act-ending example.
 * "Christmas Bells" from Rent.
 * Actually It's "La Vie Boheme" that finishes act one. All the cast, (Ensemble too) in a restaurant singing about their love of the bohemian life. Awesome indeed.
 * True, but "Christmas Bells" still counts. Every single person in the cast (at least 20 people) comes on stage, and, from the sound of things, all of them get a solo line or musical figure at some point in the song.
 * The Tony-winning Broadway musical In the Heights has two examples of this: "96,000," the major production number in the show, comes when somebody on Usnavi's bodega buys a winning lottery ticket, and everyone has their own way they would spend those earnings. Another comes in the first act closer, "Blackout," when,  Yet another example of the Crowning Music of Awesome.
 * Jekyll and Hyde has "Your Work And Nothing More", where all the main characters worry about Jekyll, except for Emma's father, who worries about her.
 * The later versions of "The Deal (No Deal)" in Chess. this also reprises pretty much every song up to this point, although not in counterpoint.
 * Gilbert and Sullivan do this all the time.
 * And, on a number of occasions, half the cast are singing one song while the other half are singing another.
 * The song "I Hope I Get It" which serves as the opener to A Chorus Line. All of the auditionees sing, in unison, about how much they need a job, that their unemployment has run out, and that they all think they've blown the audition.
 * Also "Hello Twelve, Hello Thirteen, Hello Love" which is basically a fifteen minute long reflection on adolescent experiences.
 * There is also the song "One" (at least in its finale/reprise form), in which all of the dancers, even those who had been eliminated from the auditions earlier, return to sing and dance backup for a nonexistant star.
 * Urinetown does this from beginning TO END.
 * Bat Boy the Musical has Comfort and Joy, which ends Act One.
 * Curtains has many of these, but the one that best fits the trope is "He Did It" from the beginning of Act 2, when everyone reacts to.
 * "Getting Ready" from Thirteen, as well as "A Little More Homework" later on.
 * "Man Up" from The Book of Mormon
 * An interesting twist on this trope can be found in the musical adaptation of The Secret Garden - the "Quartet" at the beginning of Act II juxtaposes Archie and Neville's feelings about Archie's current loneliness after Lily's death with a flashback to Rose voicing to Lily her objections over her impending marriage to Archie.
 * "I Can't Imagine" at the end of the first scene in Vanities has the three characters singing about their upcoming college life, complete with a counterpoint trio section.
 * Aida has two of these. "Not Me", towards the end of Act I, between Aida, Mereb, Radames, and Amneris, where Radames goes through a realizaiton that he wants to help the Nubians, which confuses Amneris and Mereb and delights Aida.
 * The second is called "A Step Too Far", which acts as the introduction to Act II. It's done very simply, with everybody in simple black costumes in front of a field of stars. Aida describes her issues with having to fight for her people, Radames discusses his troubles with being engaged to Amneris but in love with Aida, and Amneris talks about her failing relationship with Radames. Each person wonders if they've taken a step too far out of their normal place, and will it end well for them.
 * In Drood, the 1986 musical adaptation of The Mystery of Edwin Drood, there is a song called "No Good Can Come From Bad," in which the violent motivations of all the principal characters are revealed before Drood dies.

Web Original
"Captain Hammer: This is so nice / I just might sleep with the same girl twice / They say it's better the second time / They say you get to do the weird stuff. Groupies: We do the weird stuff. Captain Hammer: (Aside Glance)"
 * The Epic Song of "Gotta Get Back to Hogwarts" from A Very Potter Musical, which brilliantly sets up the Alternate Character Interpretation, humor, and some plots. Harry, Ron, and Hermione are returning to Hogwarts, Harry meets Ginny who instantly falls for him but he's interested in Cho, who is dating Cedric. Malfoy arrives and teases them and reveals his motive of finally beating Harry. The gang all gather and ride the Hoqwarts express to Hogwarts where they are greeted by Dumbledore. And all in all there's a general agreement that this year's going to be totally awesome. And this is all just the opening number.
 * Also, later in the show, Ron and Hermione lead the entire cast in The Song Before the Storm to say that Voldemort is Going Down.
 * Me and My Dick has "Ready to Go", the second song in the show. Sally and Miss Cooter want Joey, Sally asks Joey to be her science partner, Joey and Dick pine for Vanessa, Flopsy is sick of dicks, Tiffany Really Gets Around and so does The Old Snatch. Vanessa has dumped her cheating boyfriend and Tiffany plans for Vanessa to seduce Joey to get back at him.
 * "So They Say" from Dr. Horrible's Sing-Along Blog gives us the villain, hero, Love Interest, and a whole host of minor characters all discussing the upcoming action of Act III, with several, mainly humorous counterpoints, especially the cuts to Captain Hammer's groupies.


 * The Phoenix Wright Musical Project has one as the opening song. "August Day" features Phoenix Wright, Jack Hammer, Lotta Hart, Detective Gumshoe, Maggey Byrde, Cody Hackins, Penny Nichols, Furio Tigre and Mia Fey all showing a defining character trait in regards to the upcoming trial.
 * At the end of The Nostalgia Chick's review of Les Misérables, she and a bunch of other That Guy With The Glasses reviewers sing "One Day More".

Western Animation
"Bloo: I am Bloo, and you are my minions! Alone, you are all just knockoffs of a really cool guy, but together, we are stronger than any army! I think you know what we must do... That's right! We must all sing the theme song from the Ice Charades in 100-part harmony!""
 * "I'm Moving On" from Teachers Pet.
 * From the Foster's Home for Imaginary Friends episode "Bloo's Brothers":


 * "At The Gala" from My Little Pony Friendship Is Magic. The song is even based on "Ever After" above.

Opera
In opera it's often "the ensemble song before the break" or the finale.


 * Aida, Act II finale
 * Don Carlo, auto-da-fe scene
 * Il Trovatore, climax of the monastery scene
 * La Traviata, Act III finale
 * Turandot, EVERY act's finale
 * Otello, Act III finale
 * La Boheme, Act II finale ("Quando m'en vo" / "Chi l'ha richiesto?")
 * Peter Grimes, inn scene climax (characters arriving one by one or in small groups till everyoen is on stage)
 * Billy Budd, battle scene
 * Rigoletto, curse scene
 * Marriage of Figaro, Act II finale - they keep coming and coming and then nearly everyone is on stage
 * Don Giovanni, Act I finale, Act II sextet, Act II final sextet
 * Un Ballo in Maschera, Act I finale, Act III finale
 * Carmen, Act II finale
 * Boris Godunov, "revolution" scene