I remember seeing this and it looked awesome
I wonder if the engine could be speeded up in some ways or if it's due to the grayscale? I made a 4 level grayscale map engine once and it ran at 2 FPS on a SE calculator (I could have made it faster but I had the grayscale so it looks almost flickerless), but it had no masking and no scrolling. I also lost the entire engine
(it was back in late 2008 and was meant to be included with Nitacku grayscale ditherer)