The bar in the middle of the screen is the HP of the ship. Lizards' explotion will deplete the bar gradually. If the bar is emptied, a 60 seconds countdown timer will start. If you failed to kill both bosses when the timer is up, the ship will be destroyed and cause party wipe.
Boss Skills:
Tail Swipe: Painful for chars with low defense.
Tornado: Cast a tornado which moves linearly.