Board Thread:General Discussion/@comment-29742364-20170812013747/@comment-28517148-20170918073452

''...Humans are unbelievably strong. It would take the SOUL of nearly every monster... Just to equal the power of a single human SOUL... and ...Anything can enter through the seal, but only beings with a powerful SOUL can leave...'' - Ancient glyphs. The question is: what powerfull really means? Also, during phone call Sans says you made a snowman really happy which refers to Snowdin Forest NPC that wanted to take the piece of them to the ends of the earth. All above gives hints that Frisk is not only capable of crossing the Barriel but also states that they actually has done this. So yes, Frisk has left the Underground.