I feel silly. I can kill the goblin chief, but after that I can't go anywhere.There are xichrons visible on the left, but...what to do?
You can use the tree trunk spell that you just got after beating the goblin to climb up the wall and get the Xichrons. (As far as I remember)
To reach the exit you have to use the tree trunk spell and climb up the left side
wall...but don't miss the power-up on the right side as well!