If you see this video’s description. You can probably understand why it has “Music in this Video” at the bottom of this description. YouTube’s Content ID system has selected this video to be monetized with royalties going to Materia Music Publishing, the estate responsible for managing the use of the music for Undertale and Deltarune.
Under Materia’s free, limited license, they strongly ask that you not dispute in order to support Toby Fox. Having the video be monetized on our end would require us to go through a copyright strike and counter-notification or be forced to pay expensive licensing fees. That said, a number of other Undertale and Deltarune-related videos are being hit with Content ID claims for music use.
We don’t have time to explain this, so if you want to learn more on how to create Undertale and Deltarune without getting hit by a Content ID claim or be forced to go through licensing, please read a similar guide we put out for Touhou Project and Rightsscale.