It is called Uppertale! Instead of starting out as a human (like in the original game), you’re a monster! This game is short, but there are more chapters coming soon, so stay tuned!
Also, if you have any questions, then you can ask them.
Ive made a bossfight creator on the Devlog topic on in game if anyone wants to make there own bossfight in Uppertale. So check out the devlog version through this link: