Dennis will use Sponge Bob as a hockey stick and hit toilets at you (which means you are Patrick). If you upgraded Pat's Star Spin, use it to hit them back at him. The entire battle remains the same, except after a chunk of his health is gone enemies will appear and spin attack you. Jump on their heads. In part two of the battle, you will be Sponge Bob. Dennis wil throw daggers at you. Just dodge them. Attack him with a Bubble Bowl. Again, the fight is the same, only fish with giant crowbars will try to hit you. If you upgraded your Bubble Bowl, detonate it between Dennis and an enemy if they are close.