Instructions
Watch the cut scene that establishes the fight, but be ready to move. Crousteau will attack as soon as the scene ends.
Run directly at Crousteau and hit "B" to use your Stop Time spell as soon as he opens his mouth.
Fire a few shots into Crousteau's mouth with your Ion Detonator. Press "B" again to start time again and let Crousteau take the damage.
Avoid Crousteau's tentacles by jumping around the map and using your jetpack. You will have to wait for your Stop Time spell to recharge before attacking again.
Fire your weapons at Crousteau's head until his shield breaks. The Disintegrator Ray is the most powerful option in this particular fight. Once the shield breaks, the next fight phase will begin.
Wait for Crousteau to lob a fireball at you, and then hit "B" to stop time. Press "Y" and "L" simultaneously to activate your PK skill and force the fireball back into Crousteau's face.