Thanks for playing!
Making the shader be also pixelated would require it to be a lot more complex. I think it is not about just rendering at a lower resolution, since shaders work with the pixels on screen, but I am not a shader expert. It could have made a cool effect, but that went beyond my abilities.
The ambient light could not work, since the ghosts are meant to be hidden. I did thought about adding torches that shine a bit, but that also meant changing the shader.