Playing the normal version, I could not work out what was going on. However, with the little map to show how it works, I can see what you're trying to accomplish.
Rendering definitely needs work, particularly where mountains overlap and hills are seen in the distance.
A higher
key_repeat_interval would be appreciated, say
0.5. (See
Prelude.)
Maybe the edge of the map should be drawn as a chasm?
I was also confused by being able to walk through mountains. They look large enough to be walls.
What you have there is an amazing effort! I hope to see this polished.