The floating skull is the last part that will go on. I just thought a floating skull doesn't look that impressive, especially if it the big bad boss the heroes have no hope at all of defeating.
"Oh look, a skull"
"Um... Are skulls meant to have laser beams coming out of their eyeballs"
"Why aren't you answering, oh you've been severed in two by those laser beams, this may be more than just a floating skull."