Board Thread:General Discussion/@comment-28925112-20160730202210/@comment-29436648-20161016030550

DiscoFoxy325 wrote: I personally think they each died here

Light Blue Soul:Ruins

Dark Blue Soul:Doggo ( Snowdin)

Orange:Papyrus ( might have spelled it wrong)

Green soul:Undyne

Purple:Muffet

Yellow: Mettaton

Well extremely unlikely that Papyrus, Undyne, and Mettaton. Muffet and Doggo I'll give it a past but like I said in my other theory is that Papyrus haven't seen a human before which means back then he might've been a child and Undyne probably be the same age as Papyrus. Mettaton though is an absolute no due to the fact during that time he's was still getting his body or more likely still a ghost. The reason I believe that is what Toriel mentioned in the beginning of the game is that a human haven't arrived in the Underground for a long time which at the time the Yellow soul arrived it is most likely the time before or during the experiments Alphys was doing (which spoiler alert) injecting the dead corpses of monsters with determination which is mentioned in one the of the logs is that Alphys was still making Mettaton's body.