This is a fan game being made by a person called MasterSword and other developers. I'm really excited about it because it looks really good so far. You play as the child with the yellow soul. Which in Undertale leaves a cowboy hat and an empty gun. We know this because in the Omega Flowey fight, the yellow soul tries to shoot you with a gun. Look at the description of the video and the creator's FAQ comment on YouTube to find out more.
* You're filled with Justice
Video by MasterSword
