Originally Posted by Mrs Beanbag
Another way to deal with this issue is to draw all the bobs "behind" the tilemap, as is done in Chuck Rock and other games using that engine. Presumably (i'm guessing) it also maintains a mask as it scrolls on another invisible bitplane, and combines that mask with the bob's mask. That way, to remove the bob we can just blast it off in colour 0 using the same mask again and we don't need to worry about restoring the background at all.
I was reading this wide eyed trying to make sense of this "just blast it off in colour 0" statement until I watched a video of Chuck Rock and realized the game uses dual playfield. Quite an important detail.
And to add to the list of techniques which save time when drawing bobs.
The fastest behind-bob background redrawing routine is the one ... you do not call.
I'm sure you will figure it out very quickly if you dedicate a few neurons to the idea.