Update (1/3/2020): Power Your Fun has responded to TheGamer with the following statement.

The Toby Fox song was programmed into the initial batch of the product by the manufacturer without our knowledge of its origins. We are currently in the process of securing the rights to the song, “sans” to use in our product as we move forward. In the meantime, we thank you and our diligent customers for bringing this to our attention.

Basically, it seems like Power Your Fun isn’t going to stop production. Rather, they intend to keep using “sans.” and get official permission from Toby Fox. It’ll be interesting to see where this goes.

Original Story

Sans from Undertale is often associated with the “Megalovania” track that plays during the battle with him at the end of the Genocide run, but he does have a separate theme that bears his name. The track that plays during most encounters with Sans is called “sans.”, which was originally created by Toby Fox for a project related to Homestuck. 

The one place that an Undertale fan might not expect to hear “sans.” is from a robot toy unicorn that a family member received for Christmas. A Twitter user named BiancoAsterisco uploaded a video showing a toy unicorn playing “sans.” as it moves around.

Any thoughts of the video being staged were quickly gone when someone in the comments linked to a video uploaded to YouTube by the toy manufacturer, named Power Your Fun. The “sans.” song can be heard at the 2:20 mark.

So, what is actually going on here? Toby Fox has never mentioned this toy on any of his social media accounts and there are no copyrights for anything Undertale related in the product descriptions or manuals for the toy, so it’s definitely an unintentional use of the song. It’s possible that the toy uses parts that had been purchased from China and that the music was pre-loaded into it, with the manufacturers being unaware of its origins, though this is only speculation at this time. The Gamer has reached out to Power Your Fun for a statement and we will update the story if they respond.