Terror of the Deep
This entire level is played out underwater. Instead of the Arwing, you operate the Blue Marine - a submarine with an unlimited amount of torpedoes. Torpedoes function like bombs. If a targeting reticule appears, the torpedo will attack there. Otherwise, it acts like a bomb. They also serve as a source of light. About a third of the way through the level things will get very dark and enemy-riddled; be vigilant and shoot as much as you can, grab as many silver and gold rings as you can, and continue to shoot torpedoes nonstop. Unfortunately, you still can't fire more than one at a time. Be careful when you go through the crevasse as it is filled with exploding starfish and, towards the end, falling rocks. You need 150 points to earn the medal.
The boss of this level is a clam-like "bio-weapon" that comes up rather suddenly. At this point long snake-like enemies will come out of the odd cylinders at the top; shoot the snakes and the cylinders now so they won't bother you later. When the clam opens up, shoot at the two fleshy strings connecting the top and bottom of the shell. When they change color, fire a torpedo at one so that it breaks, then do the same for the other string - the top of the shell will come off. Now you must shoot the membrane covering the eye and then the eye itself, while avoiding the pearl-like bullets the clam fires at you. Do this until the shield meter empties.