This level is a boss fight, and you're up against a giant, angry fish. Keep hitting the jump button to swim up, or press nothing to rapidly descend. The fish is surrounded by several bubbles, all of these need to be destroyed before you can actually damage the boss. Colliding with the boss is not what you want to do, as it does far more damage that the blue projectiles the bubbles fire off.


Once the bubbles are gone, you can finally hurt the boss. This is easier said than done since it's hard to keep track of where it is on the screen, and you will often end up colliding into it. The only attack the boss will do is throw out purple projectiles, which move slowly and don't actually do that much damage. Keep trying to land hits whenever you see the fish, it won't be a quick fight, but eventually you'll kill it.