Sector Y Combat Zone
Sector Y is the first hard level in the game (it's the beginning of the hardest game "path".) In this level, you must destroy the robot-like enemies that take several hits to destroy in addition to less hardy enemies. At the end of the level here you will face a boss actually consisting of three separate bosses; first, two of the robots that together make up the first boss and therefore share a shield meter; second, a larger, faster robot that can dock on a ship and shoot at the team from there in addition to flying around the playing field. 150 points wins the medal, and if you complete the level with at least 100 points you can advance to Aquas.
To defeat the first two boss robots, simply shoot at them until they explode; then do the same with the third robot. However, watch out as he moves very quickly; to make it easier, wait until he lands on his ship, at which point he will stay stationary while you shoot him. If you are lucky, nailing any of these three robots with a direct hit with a bomb will knock off half of the entire shield bar. This means you can destroy one of the first two robots with a single shot.