When your special meter is full, press L2 and R2 at the same time to execute your special automatically.

Note: If the screen says "Times 2" then press those buttons twice.

Here is a way to play as the hidden boss Zankuro! To select him, choose Vs. Mode and go to the Character Select Screen. Hold down the Start button and highlight the following characters in order: If your player 1 you should already be on Haohmaru, and then go to Ganjuro, Basara, Kyoshiro, Ukyo, Rimruru, Haohmaru, Shizmaru, Nakoruru, Hanzo, Amakusa, Gaira, Galford and then Shizmaru. Keep holding Start and then press X and Circle at the same time. If done correctly, Zankuro will appear as a selectable character.