[S] does move the blocks faster but any seasoned modern tetris player will want to do what is called a hard drop, instant slam to the floor. Then you have to ask does the path of instant floor slamming collide with  the snake or do you permit the snake path uninterrupted. It seems the latter would be the best as a co-op it would  be very annoying to have the tetris player quick slamming the snake. Also If I were the snake player I would want a speed boost with a cooldown. so I could press maybe right shift or ctrl or some key and boost out of bad situations if I have not already used it recently.

I am just listing off wish list items now....