Thanks for playing first of all, sorry you weren't able to get particularly far and yeah drawing is hard, though admittedly I still need to fine-tune the system it was not exactly where I wanted it to be in terms of intuitiveness, but that required outside testing we did not have time for in the end, lessons for next jam.
I REALLY wanted to add combining spells at some point, or even more runes you can cast, and I still do, and that was one of the ways I thought to implement it so yeah definitely gonna look into doing that.
Also in terms of what to do, heat the goo as much as you can to make it burn everything, but the goo also burns you so you need to cool it down to walk on it. You also need to complete the side mission of getting the schematics (a folder somewhere in the level). Once you have that you can leave via the fire exit. Hope this helps if you decide to replay!