Thanks for playing! The slime should be in the first room on the right - essentially right next to the mace. If that room was empty for you, then please let us know so we can look into why that's a bug! But congrats on getting the good ending!
Viewing post in Curse of Nowhere jam comments
Oop, found him. I did see that door the first time, but my hand phased through the handle so I assumed it was a decorative door. The next door that leads to the first skull fight is the only option, so I figured out how to open the door properly, but didn't think to check that first side room again after dying. Maybe some kind of hint pointing to that room would help?