Musical Nod

A subtrope of Continuity Nod. Most often seen in video games, this is music from a related work that is used at some point. Differs from Recurring Riff in that a Musical Nod is used far less, and generally not under the same circumstances it was originally used. However, the new use may be related; one game's random battle theme could be used for a single boss battle in a later game.

Anime & Manga

 * In Monster, "Over the Rainbow" is referenced as the song Vardemann's father played on his radio station. When Vardemann finally faces the fact that his father was a spy, and decides to deal with the trust issues this inspired in him, an instrumental version of the song is played in the background.

Film

 * In Mystery Science Theater 3000: The Movie, during one of the intermission sketches, Mike activates the Satellite Of Love's manipulator arms. The button to turn on the arms is labeled "Manos"; when Mike pushes it, the trademark Leitmotif (aka "the haunting Torgo theme") from Manos: The Hands of Fate can briefly be heard.
 * The very end of the new Star Trek film uses a lushly orchestrated version of the original theme, and then juxtaposes it with the movie's theme. Awesome Music if ever there was one.
 * A trailer for the newer version of The Karate Kid has "You're the Best Around" playing on a radio in the background for a couple seconds.
 * In Casino Royale, the classic James Bond theme is not played until the very end. This symbolizes the newly-promoted James Bond becoming the badass secret agent we all know.
 * The reveal of Brendan Fraser's car in Looney Tunes: Back in Action as  is accompanied by a quote of the theme from a certain past collaboration by director Joe Dante and composer Jerry Goldsmith.
 * The remake of The Parent Trap has Annie (?) humming "Let's Get Together" under her breath in the hotel.

Live Action TV

 * The Doctor Who mini episode "Time Crash" wherein the Tenth Doctor meets his Fifth incarnation has a Leitmotif reminiscent of the music of the Fifth Doctor's era play intermingled with the music more typical of the newer series.
 * In the Mr. Bean Christmas episode, the music Bean hums while playing with the toy marching band is clearly the opening march from Blackadder Goes Forth.
 * While it was not used in the televised episodes, the Star Trek: The Next Generation finale All Good Things... would have featured a reprise of composer Dennis McCarthy's theme for Judge Q's entrance in Encounter at Farpoint. The composition did appear in an album later on.
 * The theme music from the original Battlestar Galactica Classic plays over a human-interest news piece featured in an episode of the reimagined series.

Music

 * Occurs in at least two music videos by the band Foo Fighters.
 * At the beginning of the Monkey Wrench video, a muzak version of Big Me, a single from their eponymous debut album, plays in the elevator.
 * At the beginning of the Learn to Fly video, a muzak version of Everlong, a single from The Color and the Shape, plays while the plane is being cleaned.
 * The organ lead-in to George Michael's "Faith" is the melody to his earlier Wham! hit "Freedom".
 * Many arrangements for the Florida State University Marching Chiefs incorporate the school's famous "War Chant".

Video Games

 * Final Fantasy I for the PSP does this. The game features four bonus dungeons, with each one having a collection of bonus bosses from Final Fantasies III, IV, V, and VI. Each one has their appropriate boss theme from the game they are from.
 * Mog's Leitmotif from Final Fantasy VI later appears as the theme song of Moogles in general in Final Fantasy Crystal Chronicles.
 * Mog's theme itself is a remixed version of Final Fantasy V's Moogle Theme. Variatons of the same song are also found in IX, XIV and Type Zero
 * Dissidia Final Fantasy features music from previous games in the series, usually as battle music. However, the Overworld or Map themes from every game in the series are used in the every character's story mode.
 * In Final Fantasy VIII, the boss battle theme Premonition begins with a snippet of the main theme to Final Fantasy VII. Also, the Balamb Garden background music contains a line from the opera from Final Fantasy VI.
 * It's also used in Final Fantasy IX at least once; the Castle Pandemonium theme in that game is a slower organ version of the Castle Pandemonium theme from Final Fantasy II.
 * Fire Emblem has a few of these, in addition to the themes for arena battles being the theme's from previous games, the 6th game's "Wyvern Generals" battle theme includes both first and second games battle themes, Light and Dark from FE 4 reappears as the trail map theme in FE 9.
 * Super Mario Galaxy reuses the "Koopa's Road" theme from Super Mario 64, and the "Battelship Raid" theme from Super Mario Bros 3. The Athletic Overworld theme from the same game as the latter and a bouncy remix of the original Super Mario Bros theme also show up.
 * The sequel, Super Mario Galaxy 2, reuses the aforementioned Koopa's Road and Battleship Raid themes, plus the Athletic Overworld and Haunted Mansion themes from Super Mario World, the Bob-omb Battlefield and Rainbow Ride theme from Super Mario 64, and just about half the entire soundtrack of the original SMG.
 * The Mario series loves doing this, New Super Mario Bros Wii has a nod to the Super Mario World Castle theme in its own Castle theme.
 * There's also the Superstar Baby Mario theme in Super Mario 64, the Luigis Mansion theme in Mario & Luigi: Superstar Saga, and earlier than that, the theme for the first game showed up in Super Mario Bros 3's music box.
 * Ace Attorney 3 reuses the first game's Apollo Justice uses the original "Objection" theme when Phoenix objects in the first case )
 * In the fourth case of the third game,
 * A version of the bicycle theme from Pokémon Red, Blue, and Yellow was used as the Pokemon Catching Contest theme in the Gold, Silver, and Crystal versions. Similarly, the Ruby, Sapphire, and Emerald versions had the Marine Museum, the background music for which was a slow version of the S.S. Anne theme from RBY.
 * Inexplicably, the theme that plays when you're first starting a new game in Pokemon Battle Revolution is a more upbeat version of the Relic Forest theme from Pokemon Colosseum and Pokemon XD: Gale of Darkness.
 * Upon reaching Kanto in the Gold/Silver/Crystal versions, the Trainer battles start using the Red/Blue/Yellow theme as opposed to the new one used in Johto. This was retained in HeartGold and SoulSilver.
 * All but the first three of the Sevii Islands in FireRed and LeafGreen have music from Gold/Silver/Crystal -- Azalea Town's theme on islands Four and Five, Violet City's on islands Six and Seven, and the Route 42 theme on the interconnecting routes.
 * The Platinum/HGSS Frontier Brain battle themes have Emerald's Battle Frontier "main theme" stuck somewhere in the middle. Start listening around 0:50.
 * In the Mother/Earthbound series of games, many of the songs are either outright recycled, or make a cameo appearance in one way or another. Pollyanna, Snowman, and Humoresque of a Little Dog to be specific. The plot coupons from the first two games, (Queen Mary's Song/Gigyas's Lullaby, and the Sound Stone Melodies, both known as The Eight Melodies in each of their respective games, due to each melody being split into 8 parts.) are frequently remixed into other songs related to the Mother Franchise. (Queen Mary's song appears in the battle theme for Onett in Super Smash Bros, and the two themes are mixed into a song called Sixteen Melodies for Mother 3.)
 * It's justified in Mother 3, since most of the songs heard from Mother 2 are there due to
 * Castlevania does this a lot. For instance, the first-level musics from the first three games frequently get remixed and used again in later games in the series.
 * Castlevania: Circle of the Moon was notorious for this; only three or four songs in the whole soundtrack were actually original, the rest being from previous games in the series.
 * It's used much better in Order of Ecclesia, in the game's intro. When the opening text scroll mentions the Belmonts, a little snippet of Vampire Killer (the first level music from the original game) plays.
 * Uninvited for the NES featured a room with an old phonograph. If the player used the phonograph, they were treated to a bizarre, off-key rendition of the Shadowgate theme.
 * Oddly, the level 8 theme from Descent quotes "The Death of Åse" from Grieg's Peer Gynt suite. Huh.
 * This occurs in The Legend of Zelda series.
 * In the King's Tomb in Minish Cap for Game Boy Advance, a remix of the original NES dungeon theme plays. And, more importantly, the NES's five-note "item appears" jingle appears here for the first and only time in the game.
 * Witch Syrup's theme is rearranged from her shop music in the Oracle series, also appearing as the Witch's Hut song way back in The Legend of Zelda Links Awakening.
 * Listen very carefully, and one can hear a snippet of the Goron Lullaby from Majoras Mask in the background music of Twilight Princess' Goron Mines dungeon. The Howling Stones also use a few Ocarina tunes from the previous games, like the Song of Healing, and Requiem of Spirit.
 * Wind Waker does this several times, too, such as on Outset Island and Forest Haven (contains variants of the Kokiri Forest theme, as well as Saria's Song for the latter) and the Ballad of Gales (Minuet of Forest).
 * At least one NPC hums the "item get" music when giving you a heart piece.
 * "Into the Wilderness", the Opening theme of the first Wild Arms game, had been continuously remixed throughout the series, having been used as background music, boss battle music, and post-battle music.
 * Also, the main theme of Wild Arms 2 is played in Wild Arms 5 when the cell phone belonging to the Expy of Ashley rings.
 * Pulse Man's Neo Tokyo theme was remixed for the Pokémon DPP rival theme.
 * Super Mario RPG's Bonus Boss Culex's battle theme is a remix of the Final Fantasy IV boss music.
 * Related, the Rose Town theme from Super Mario RPG was recycled as the menu theme for one of the minigame modes in one of the later Mario Party games.
 * The Magma Mountain level from the original Mario Party incorporates the Bowser's Keep BGM from Super Mario RPG.
 * Persona 3: FES has the pre-main menu song used in Persona 4's class trip.
 * The Persona 3 song 'Joy', that plays during most of the Social Link scenes, is used in the opening scene of Persona 4's class trip. Fitting, considering makes a prominent appearance.
 * When the group visits Club Escapade at Paulownia Mall, the band on stage is playing "P3 Fes," the opening theme of the updated edition Persona 3 FES.
 * Likewise Persona 3 Portable plays Persona 4 music playing during the Female Main character's trip to Inaba.
 * For that matter, you can ask Fuuka to play various music tracks from Persona ("Persona" and "Snow Queen") and Persona 2 ("Time Castle" and a dramatic version of "Maya's Theme.") Notable in that the original game's Snow Queen Quest was axed in the rather bad English translation, and thus its musical theme was only present as FES' "BGM 01" (until Persona's PSP Updated Rerelease.)
 * Mega Man 2 has a very nice musical nod: The opening theme is a remix of the ending theme for the first game.
 * The music that plays at the very first mission of Mega Man Zero is a remixed version of the eponymous character's Badass Leitmotif from the first Mega Man X game.
 * At the beginning of Metal Gear Solid 2: Sons of Liberty, the Alert theme and boss battle music incorporated parts of the Alert theme from the first game.
 * The background music from the first Metal Gear game for the MSX was used in the VR Training segment of Metal Gear Solid.
 * Another Code R starts using the music from the first game during the final few chapters, starting with a particularly jarring moment:
 * The Norfair Ancient Ruins theme from Super Metroid has played in many, many fire-based areas over the series since (Magmoor Caverns from Metroid Prime being an example).
 * Explorers of Sky uses the background music of Ravaged Field, Magnetic Quarry, Thunder Meadow, Mt. Discipline, Furnace Desert and Jungle (all from Red/Blue Rescue Team) as the dungeon music for Southern Jungle of Team Charm's special episode.
 * Chrono Cross uses Lucca's Theme for its victory fanfare.
 * The overworld theme for the Home dimension is also a tropical-sounding remix of one of the 1,000 AD pieces of map music (i.e. the one that plays when away from towns) from Chrono Trigger.
 * In the various guest Bonus Boss instances of tri-Ace games (e.g. Lenneth and Freya in Star Ocean 3 or Gabriel Celeste in Valkyrie Profile 2) music from their original games will play. The Bonus Dungeon of Valkyrie Profile also shares a theme with the Maze of Tribulations from the Star Ocean games.
 * Spore has one during the civilization and space stage when ever you hover over a city that isn't yours..
 * Banjo-Kazooie: Nuts 'N Bolts has this all over the damn place. Virtually every single piece of music from the game has nods to songs from not only previous games in the franchise itself, but also from other games made by Rare like Conkers Bad Fur Day and Donkey Kong 64.
 * The Starbase stage from Turtles in Time uses an arranged version of the music from Krang's ship in The Manhattan Project.
 * The final segment of Sonic Adventure's Windy Valley is accompanied by the Green Grove theme from the Genesis version of Sonic 3D: Flickies' Island. Likewise, the latter's Panic Puppet (Act 1) theme is used in the former's Twinkle Park level.
 * Related to the Sonic series: the Speed Slider boss theme from Knuckles Chaotix appears in Billy Hatcher and the Giant Egg, as the music for Circus Park's night stage. Mariko Nanba composed music for both games.
 * In Sonic Generations, the solo of Classic Sonic's remix of Escape from the City is the beta version of the theme, plus the second verse gets auto-tuned to the melody of Endless Mine.
 * The hang gliding music in Pilotwings Resort contains snippets of its counterpart from Pilotwings 64.
 * The fanfare when the boss door opens in Donkey Kong 64 is an arrangement of the one that accompanies the elusive "Stop-N-Swop" items from Banjo-Kazooie (both games were composed by Grant Kirkhope).
 * Mushihime-sama Futaris Stage 3 BGM, Shinjuu Forest Rebel Army?, takes a page out of Mushihime-samas final stage BGM, The One Who is Always in the Forest.
 * In Do Don Pachi DaiFukkatsu, a somewhat different version of the stage BGM plays if you access a hidden path in stages 2, 3, or 4. In Stage 2, the music shares a phase with "Colored Rainbow", the stage 2 BGM of DoDonPachi dai ou jou. Stage 3 borrows from the stage 3 BGM of the original DoDonPachi.
 * Paper Mario:
 * The music that plays on the Bullet Bill bridge in Koopa Bros. Fortress is the airship theme from Super Mario Bros 3.
 * The music that plays during the train ride between Toad Town and Mt. Rugged is a remix of the Kalimari Desert theme from Mario Kart 64.
 * The music for Yoshi's Village is the title theme from Yoshi's Island.
 * The theme song of The Elder Scrolls V: Skyrim incorporates musical elements from previous iterations of the Elder Scrolls theme, notably a similarity to the drums of Morrowind's theme and a segment of Oblivion's theme near the end (about 3:00 into the Skyrim theme, the original musical cue comes from this segment of the Oblivion theme.)

Western Animation

 * The first episode of Re Boot features a distinctive theme for the Space Game in its first episode. The theme is brought back much later on in the episode System Crash when the User from that game emerges in Mainframe.
 * Episode 4 of Scooby-Doo! Mystery Incorporated has Daphne humming the theme from The New Scooby Doo Movies as she knits an ascot for Fred.