If you don't press A or B at the right time, the enemy stops the attack and you don't gain any cc. If you fail to match the correct button or run out of time, you will have to press B at the right time to continue the attack or press A to cut your losses and gain any cc for the successful inputs you do made. The higher the number of stage attack card, the more button presses will be required.
Comet Z is another tag move for Jeice and Burter which is a special defeat and Gotenks has Buu Ball Slam which is also tag team special defeat).
On the flipside, Burter doesn't have a signature beam move (he can use Purple Comet together with Jeice in tag team mode).
