Swamp Cage Clip
In the Kelp Swamps, there is a spatula trapped inside of a cage. There is a button that raises the cage, revealing the spatula. Patrick can toss a freezy fruit into the goo, allowing him to reach the spatula in time.
Using Lag Clipping, SpongeBob can wedge himself between a rock and the cage, then clip through the cage and the ground. The spatula will be collected and the player will fall through the floor and drown.