Board Thread:General Discussion/@comment-26006155-20181229180615/@comment-26006155-20190127010701

It's hard for me to look at this, and now think that Sans was always a good friend of Toriel, and gave her his old phone, complete with the special key to his room.. KNOWING that Frisk would use it one day.

Pre-knowledge of events. Something only a Time Traveler like Sans would have.