Thanks a lot everyone!!! Greatly appreciated!
And yes, indeed, there is sprite occlusion (which is what takes most of the CPU at each frame). I calculate a mask based on the objects around the player, and then cut out the sprites of the player, and transfer them to the VDP again at each game frame. The upside is that the main character looks very colorful (it's made out of 6 sprites), but the downside is that I can only have 1 character at most in the screen, as more than one would result it a lot of flickering, and maybe slowdown. But it worked out at the end! 
And thanks @tfh!! One little detail, it's "Westen" (without the "r"), the spell checker keeps trying to insert an "r" there haha
And thanks @tfh!! One little detail, it's "Westen" (without the "r"), the spell checker keeps trying to insert an "r" there haha
LOL.. I guess that's what happens when you do things in the morning on your laptop without your glasses.
I've fixed it as far as I could without breaking all the links I've posted ;-)
That looks great! Well done