I wanna crack a joke about Dr. Mwho? Or perhaps a Luigi version, but then again I have always been more of a weegee fan anyway.

I already mentioned fading the boo in to the background more. so their is that.

I think you could also benifit from a stronger shadows. by pushing tinbs more in to the dark and having a focused light source you could give off of a more "single light source in a haunted house feel."

I really like the wide eye bit you got going on there with Dr. M I think it is the good start to an expression to go with the don't blink theme.

I like the shadowing you got going on with the mouth of boo. it has alot of the stronger shadows I was mentioning about doing on Dr. M

Over all I think this is a good improvement over past works. Your lines are cleaner and your coloring and shading are smoother.
Congrats man, keep it up