But, there is a lag when getting the hammer and also when it goes away.
And the left side of the the background scroller kind of flickers.
Sometimes it changes, then the right side flickers.
It's an issue with the way the OP works, I'm using a 256 pixel resolution but the OP renders a few more pixel, also I don't have any clipping code and on the right side of a sprite you can't clip with pixel precision.
I'm going to fix it drawing two black strips on each side to display only 256 pixels, this was in my TODO list long time ago XD but I need those extra pixels to see the CPU usage changing BG register.