The fact that I had to go into the game files to change the battle music so I wouldn't get mass copyright claimed on my Undertale Yellow videos is absurd. This doesn't happen for literally anything else.
This is what they told me when I asked them to release the claim btw
Let's unpack the music of Undertale Yellow!
I don't speak for Toby/Royal Sciences, who hold multiple trademarks and copyrights.
I'm not an attorney, this is not legal advice; this is general insight into the graces by which fangames of non-litigious rightsholders get to exist