Talk:Mettaton/@comment-4369608-20151222161229/@comment-27559164-20160106182439

Ghosts appear to be their own class of monster as opposed to being the soul of a departed moneter if that makes sense. They could be made in some other way, but I am uncertain about that and refuse to speculate.

An ability that ghosts seem to possess is the capability of going from a specter form to corporeal so long as they can inhabit a real object. This is actually a process that we are told about by Mad Dummy, admittedly,in a very angry manner. Napstablook also shows disinterest in becoming corporeal despite it being a very real thing they are capable of.

It wasn't so much Alphys harnessing the soul as it was Alphys building a robot without any actual programming which got possessed by Mettaton. And voila, that is how we got a ghost inside a robot.