Dark spin

From the Super Mario Wiki

Dark spin is a special move that Bowser uses in Super Mario Galaxy, on the 2nd time he is faced to destroy the Mario Bros. It is related to the Star Spin and is in effect the counterpart of Mario's move. It is a move that is very hard to predict. When Bowser uses it, Dark Matter comes out his fingers whilst spinning. If he hits Mario/Luigi, they get sent flying whilst losing some health. To avoid it, the bros. have to run away from Bowser or spin to block the matter. Note that Bowser uses this move, only when he's faced at Bowser's Dark Matter Plant.