Undertale was created by "Toby Fox"
Underswap was created by "Temmie Chang"

Undertale AU: Underswap (by Temmie Chang) (Moon's Musical Rendition)

Underswap was created by Temmie Chang

This replaces "Spear of Justice"

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Leitmotives (In-order):
-+-+-+-+-+- Part 1 -+-+-+-+-+-
-Alphys (Base + Part 1 + Part 2)
-Alphys (Beta, Part 2)
-+-+-+-+-+- Part 2 -+-+-+-+-+-
-Alphys (Part 2)
-+-+-+-+-+-  Part 3 -+-+-+-+-+-
-Here We Are (Part 2) + Amalgam (Beginning) + Alphys Part 3 (Modified)

[Undertale AU][Underswap - Alphys] Here, Duel with the Goddess of Storm!

Underswap was created by Temmie Chang

This replaces "Waterfall"

Genocide: https://drive.google.com/file/d/1PMax79f5wLbkatt-_GhqysRDpJXICgKW/view?usp=sharing

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Leitmotives (In-order):
-+-+-+-+-+- Part 1 -+-+-+-+-+-
-Another Medium
-+-+-+-+-+- Part 2 -+-+-+-+-+-
-Alphys (Part 2) + Another Medium (Part 3)
-Here We Are (Part 2)
-+-+-+-+-+-  Part 3 -+-+-+-+-+-
-Another Medium (Part 2)

[Undertale AU][Underswap - Area] Negai no Mizu (+ Genocide on the desc)

Underswap was created by Temmie Chang

*Welcome to our world, young one.
*This is the CORE part of our new home.

This replaces "Ruins"

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This track is heavily inspired by both CORE and Undertale (since it's played in New Home). A lot of symbols are put into this song. This is another one of the "Main Themes" for the AU. The more intense-sounding Ruins represents that you're welcome to the monsters world! The chord change from F# to E suggests that you'll be facing countless of troubles ahead, then it changes back to its original key to represent that they're still full of hopes for your arrival! The ending part, namely, the pretty subtle "New Home" theme played by "Undertale" is to represent Chara's brand new adventure with their theoretical theme and "His Theme" played at the same time. The violin (the lead instrument) plays the melody of a modified "Undertale", specifically in this part: 4:43-5:19 Patient plays in this segment not only because it compliments Another Medium, but also because Chara's soul would be Patience as the soul traits are reversed from Determination to finally Patience.
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Leitmotives (In-order):
-+-+-+-+-+- Part 1 -+-+-+-+-+-
-CORE (Beginning, Modified)
-Another Medium (Part 3, Modified)
-Another Medium (Part 2, Modified)
-+-+-+-+-+- Part 2 -+-+-+-+-+-
-Another Medium (Part 3, Modified)
-+-+-+-+-+- Part 3 -+-+-+-+-+-
-Another Medium (Part 2, Modified)
-+-+-+-+-+- Part 4 -+-+-+-+-+-
-Undertale (Modified)
-His Theme (Modified)
-Undertale (BETA)
-Patient

[Undertale AU][Underswap - Area] Homely Catacombs

Underswap was created by Temmie Chang

This replaces "Snowy"

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I used one of DEP songs because irl Temmie and Toby swap place and I thought it worked well considering it's a normal forest and it has OUaT melody in it. 
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Leitmotives (In-order):
-Dweller's Empty Path - Somewhere in a Forest (by Temmie Chang)
-Once Upon a Time (Potential Melody, Modified)

[Undertale AU][Underswap - Area] Leaves Fill the Path

Underswap was created by Temmie Chang

This replaces "Once Upon a Time"

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Again with the irl Toby and Temmie swap reference!
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Leitmotif:
-Escaped Chasm (by Temmie Chang) - House (Modified)

[Undertale AU][Underswap - Main Theme] Introduction of Everything

Underswap was created by Temmie Chang

This replaces "Start Menu"

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Leitmotif:
-Escaped Chasm (by Temmie Chang) - Title Screen

[Undertale AU][Underswap - Start Menu] Name Screen

Underswap was created by Temmie Chang

This replaces "Snowdin Town"

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Leitmotif:
-Dweller's Empty Path(by Temmie Chang) - Small Village (Modified)

[Undertale AU][Underswap - Area] Small Village

Underswap was created by Temmie Chang

This replaces "Shop"

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Leitmotives (In-order):
-Dweller's Empty Path(by Temmie Chang) - Buy Something Will You... Can't (Modified)
-Dweller's Emprty Path (by Temmie Chang) - Leaves Fill the Path

[Undertale AU][Underswap - Shop] Buy Something Will You?

Underswap was created by Temmie Chang

This replaces "Mysterious Place"

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Leitmotif:
-Dweller's Empty Path(by Temmie Chang) - Underground Path (Modified)

[Undertale AU][Underswap - Mysterious Place] Down the Path of Darkness

Underswap was created by Temmie Chang

This replaces "Dating Start"

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Leitmotif:
-Dweller's Emprty Path (by Temmie Chang) - Leaves Fill the Path

[Undertale AU][Underswap - Friendship] Road to Friendship

Underswap was created by Temmie Chang

These replace "Anticipation" and "Enemy Approaching"

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Yeah, this could also work for "Swapped Rhythms"
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Leitmotif:
-Stronger Monsters

[Undertale AU][Underswap - Random Encounter] Afterthought + Free-for-All Ultimatum

Underswap was created by Temmie Chang

This replaces "Heartache"

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Leitmotives (In-order):
-Bergentruckung
-Small Shock
-ASGORE
-Heartache (ASGORE arrangement)
-Stronger Monsters

[Undertale AU][Underswap - Asgore] But We Could be Like... Like a "Family"...

Underswap was created by Temmie Chang

This replaces "Fallen Down"

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Leitmotives (In-order):
-Determination (King Description Arrangement)

[Undertale AU][Underswap - Asgore] Sage of the Vaults

14th August (late) report:

Underswap was created by Temmie Chang

This replaces "Ghost Fight"

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Leitmotives (In-order):
-Death by Glamour/CORE
-Metal Crusher (Modified)

[1 Year on Soundcloud Special][3/10][Undertale AU][Underswap - Mettaton] The Show's Spirit!

Underswap was created by Temmie Chang

This first track replaces "Your Best Friend", while the rest are exclusives.

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Leitmotives (In-order):
-Mushroom Dance
-Escaped Chasm (by Temmie Chang) - Hot Demon Man (Modified)

[Undertale AU][Underswap - Ragel] Ragel + Dance Alongside the Mushroom + Freaky Fungi

Underswap was created by Temmie Chang

This replaces "sans."

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Leitmotives (In-order):
-PAPYRUS' COOL SONG
-Bonetrousle

[Undertale AU][Underswap - PAPYRUS] PAPYRUS' COOL SONG

Underswap was created by Temmie Chang

This replaces "Metal Crusher"

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Leitmotives (In-order):
-Dummy!
-Ghost Fight

[Undertale AU][Underswap - Napstablook] All That Jazz!

Underswap was created by Temmie Chang

This replaces "It's Showtime"

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Well Sega and Nintendo swap so--/
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Leitmotives (In-order):
-Spooktune

[Undertale AU][Underswap - Napstablook] Tune It Up

Underswap was created by Temmie Chang

This replaces "Alphys" (literally)

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Leitmotives (In-order):
-Spear of Justice (+ Battle Against a True Hero variation)

[Undertale AU][Underswap - Undyne] Undyne

Underswap was created by Temmie Chang

This replaces "Another Medium"

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Leitmotives (In-order):
-Another Medium
-Waterfall/Spear of Justice/Battle Against a True Hero
-Undyne

[Undertale AU][Underswap - Area] Sea of Winter

You still have no idea who I am... Ok some things about me, just a really busy 17 year-old guy who's spontaneously producing au tracks. I take requests ocassionally or when i have more free time. i work on many aus (including someone's au) and several UT fangames. I make roleswap au tracks a lot more than crossover ones. I mostly make death by glamours, battle against a true heroes, heartaches, and asgores because those are my favorites and really fun to make.

And here's my discord: MoonStriker#0730

QnA:

Q: Do you have any AU?
A: Yeah, I have: Rolled Cycle (Swapspin), Last Hope, and Underswitched. "Will I make songs for one of theses aus?" Someday, yeah. 
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Q: Can I use your musics for my au?
A: Sure! If the description of the certain music says that, then yes! I'm wary about Deltarune aus, though.
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Q: Do you have any song project?
A: I consider "Chara and Asriel swap" to be my primary music project. There's more such as "Chaos Kings" and "Doused Flames". Upcoming project might be "Toriel and Asriel Swap" or "Mettaton and Asgore Swap". I'm not sure, but you can decide which one too based on what you're interested with.
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Q: Do you take request?
A: Yes, but that depends or it'll take some time to actually do it.
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Q: What is your favorite UT music?
A: For battle theme: Battle against a True Hero goes to number one! Death by Glamour goes to second! And finally... ASGORE goes to third! Last but not least... Heartache or Spear of Justice? I don't know, both are on-par to me =P As for area theme, Waterfall and Another Medium for the win!

Source of Profile Picture's Image: https://quicksilver26.tumblr.com/post/148474219112/tokonbu-papyrus-and-sans-%E3%83%A1%E3%82%A4%E3%82%AD%E3%83%B3%E3%82%B0%E3%82%82%E3%81%A4%E3%81%91%E3%81%A6%E3%81%BF%E3%81%BE%E3%81%97%E3%81%9F

Undertale AU: Underswap (by Temmie Chang) (Moon's Musical Rendition)

MoonStrik3r