Floyd is not a naturally mobile fighter to begin with. It's not his style. He adopted the slick pot shotting style to take on big physical maulers. He looks way more comfortable with both feet planted.
In regards to the smiling, a lot of guys do it under pressure. Some even laugh a as the pressure builds. I know I always had to fight back a snicker of disbelief every time I got hurt to the face in the amateurs. See cosme Rivera Judah for a prime example.