As of 1.1 I can now reach the Slime Boss and beat her, however I can't get back out from the bottom of the map to explore the rest of the rooms because there wasn't a chandelier for me to jump on to climb out of the pit I was in.
I wish I could at least get Vivi back to her Mistr... I mean the Witch! Yes, that's what I was going to say. The Witch. Wait, what was the Artifact that Cursed Vivi anyway? And where is it right now?