Naturally, being an Undertale game, TS!Underswap comes with spectacular music. You can listen to the entire official soundtrack on SoundCloud here
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- "Fuzzy Friend", Temmie's Leitmotif, is a catchy, charming little song that plays during your first encounter with the plushie.
- "Rise, Child" is Asgore's version of "Fallen Down", resulting in an incredibly gentle, soothing song that perfectly captures Asgore as the caretaker of Ruined Home and Chara's Parental Substitute. Equally good is the piano version another team-member made.
- "Small Talk", which plays when Asgore is walking and talking with Chara through the corridor, is another bit of cheery, relaxing music that even incorporates the "ASGORE" leitmotif. It really helps showcase what a sweetheart Asgore is.
- The battle themes for the two original minibosses in Ruined Home, the Ruined Knights and the Greasers, are not only both total bops, but also help set the different tones for the battles and the new characters. "Knights! Trouble Afoot!" feels intense because the Ruined Knights are serious about capturing a human SOUL, and helps sell the Knights' anger and desperation if you've killed one of the comrades (forcing you to kill all three, as the other two will now not accept your mercy), even more so in Ruthless which gives off the feeling that they, the heroic knights, are doomed to fight a losing battle against you, the vile murderer; a complete 180 from the Greasers' fight theme, which starts off seemingly intimidating, but then becomes bouncy and playful since really they're just punks you can deal with in goofy ways and you can't kill them (since they just run away if you bring them down to zero health in Neutral or Compassion, and you don't get the chance to fight them at all in Ruthless).
- "Dummy Chase!", the song that plays when the Mad Dummy chases you, is a fantastic, even faster-paced remix of "Dummy!"
- Mettalot's new boss theme, "Stage Fright", is jazzy, fun, and perfect for the penultimate boss fight of the demo.
- "SOUL Ablaze", the boss theme for Asgore, is a remix of both "Heartache" and "ASGORE", and it's catchy and tragic, as Asgore fights to keep Chara in the Ruined Home even though Chara wants to stay, but is possessed and forced to leave by outside forces.
- We only hear a small part of it in the demo stinger, but the full version of Crossbones' theme, "Starlight Savior" sticks to the time-honored tradition of Sanses having great theme music.
- The gorgeous area music for Starlight Isles, "Stargaze". The piano is reminiscent of "Snowdin Town", but the tune and addition of more instruments create a warmer, richer feeling overall... which fits since the second area is now summer-themed.
- "Count Koffin-K", unveiled in the official September 2021 progress report as the overworld music for Crossbones' greatest foe. It's grandiose yet menacing, just what any self-respecting supervillain would want for a theme song.
- "GLOIRE SEI ADMIRAAL!" is a bombastic militaristic piece which quickly establishes Alphys as the next major threat in Chara's journey.
