Edit: Ignore my half-baked work and wait for @Kapola7 to finish their transcriptions. I wanted to highlight the necessity to renovate the page, but did things too fast with the childish thought that I wouldn't look serious otherwise.
I noticed how the Deltarune leitmotifs page has very detailed sheets for its leitmotifs, covering all the parts and variations. The Undertale page seems bare-bones in comparison.
For this reason, I suggest you new sheets that cover every main leitmotif, their subparts and variations:
https://drive.google.com/file/d/1kHcLcnZs2JyMDHQzT0TwyJWtC_dNF2Pf/view?usp=drive_link
Credits (check them on MuseScore): Z1ggyZip (Fallen Down), Nickoli_dudyo (Ruins, Heartache, sans., Snowdin Town, NGAHH!!, Hotel), HeavySquare (Enemy Approaching), Kuppa (Ghost Fight), SparklingJupiter (Shop), 2 Pts (Undyne), annoying doggo (Another Medium, CORE), Woopinah (Abandoned Town).
Better warn you about some liberties I took before any change is made:
- I proceeded like the "Girl Next Door" motif and used the name "It's Showtime" for the bassline and "Mettaton" for the main theme. It's his motif, after all.
- "Another Medium" sheets use the titular song as a basis instead of Waterfall.
On the other hand, the following sheets are the same, but with a new aesthetic: Flowey, Toriel, Sans, Papyrus, Mettaton (the one currently known as "It's Showtime!"), Metal Crusher, Asgore, Your Best Nightmare.