I don’t know much about video games, but here’s what I can tell you about Undertale: It’s a role-playing game where you don’t even have to kill anyone if you don’t want to.
And here’s a stylized version of one of the characters, Sans:
Again, he’s just a harmless video game character. He’s also the subject of a question Pat Robertson decided to answer on The 700 Club yesterday. Viewer “Payton” said he saw the character on his daughter’s phone and wanted to know how to help his daughter “not be attracted to such demonic things.”