How do I set walkable areas to be different for different characters? For example, maybe you can switch to a bird character who can fly around in the sky, and then switch to a fish character who can go from screen to screen but only in the river areas.
Simplest way is to just draw two different areas for them, but these areas won't be joint together, so the bird won't "walk" into the water and vice versa for the fish.
Slightly more complicated way, when you need the areas to be joint/overlapping, is to use the RemoveWalkableArea() and RestoreWalkableArea() to set where the character can walk on according to its state.