Clock Out is one of the special moves that appeared exclusively in Paper Mario: The Thousand-Year Door. It requires 2 gauges of the Star Gauge to use and this move is learned after Mario gets the second Crystal Star.
This move is used to immobilize the enemies for several turns in order to prepare and/or attack them. First, you must charge up the gauge, then press the button identical to the one on your enemies. Be careful because that the enemies might also also throw it back at you or the audience.