Okay so I have a theory on the egg dude. For now we will call him William D. So what if, now hear me out here, what if Will was a human. And not just any human, kris's father. Now we know that the prophecy basically tells the future to it's exact. What if FRIEND pulled a Dess Holiday and kidnapped Kris's father since it might mess with the prophecy. Then friend brought him into the bunker and like shattered him across time and space. Now what if at the same time, kris's father was also gaster. What if the Egg man was named something like William David Gaster or something. What if Will was a scientist who studied the life force, but got fired for being super dangerous. And so people took all his money or something and him and his unnamed wife who had just given birth to they're son Kris Gaster had to leave and move to home town. But they couldn't find a house since it's a 100% monster town so people will be racist. They couldn't take care of Kris since all they had to eat was moss. So they had heard good things about a family called the dreemurs and decided to leave kris at their door step...
andwhatevidenceexistsforthis
justsayingitsoundslikeaheadcannonorauorsomething
IDK non just a cool head cannon, also might explain the voice thing. Well not really, more a "Sans is Ness" type thing where it's just to change perspective
Voice gaster speaks with the player not Kris though