If you don't have a mouse, it doesn't look like you can scroll up or down. You could use the mouse wheel or right click to drag but those are both on the mouse. I will make the arrow keys do the same thing for your convenience.
Unlike the first game, enemies are based on how hight you are. Super enemies and bosses should be even harder. The altitude doesn't really do anything and its just for show but the values the altitude is calculated off of are the same ones that determine how hard enemies are.
I can't believe someone actually played the prequel! Trees may be coming back sometime, i have all the sprites ready just haven't had the time to implement them. Glad someone still remembers them.
Cheers!