Game Lock Up
From Creatures Wikia
The lock up occurs whenever an Ettin enters the Marine Terrarium and throws a star into the ocean. As soon as the star comes into contact with the water, the entire game will lock up, making it entirely unresponsive, and the only option is to reset the Playstation Console. Unfortunately, the only known way to prevent this annoying error is to never enter the Marine Terrarium once the Desert Terrarium has been unlocked.