Board Thread:General Discussion/@comment-27894627-20160511021754/@comment-5028423-20160529161226

From the "Mystery Key" page: Mabian, isn't Happstablook the ghost inhabiting Mettaton? You said "Mettaton is actually a robot body inhabited by a ghost, whose name is not stated by the game."
 * If Undyne and Papyrus are called while in the house, Papyrus dubs the ghost who Mettaton once was "HAPPSTABLOOK, THE HAPPY GHOST". Alongside this, the name of Mettaton's house in the game files is room_water_hapstablook.