When does the forest end?

You have too many octopi. They'll be preventing you from moving right. I'm afraid you'll have to abandon your progress and restart, maybe without the obsidian crown? I find it easy to get through the forest with the jasper crown and enchanted monkey staff.

As a general rule, in most levels, if you can't see the background scrolling, you're not moving and the level won't progress. This is particularly relevant in the sea, where if you wedge yourself against the ground the waves of fish won't end.