From StrategyWiki, the free strategy guide and walkthrough wiki

Rewards

• Wide Cannon
• 10 Bullets

What to take

Still not much choice yet, but you must take the basic gun, the red transmitter, and the flare bombs. It would be nice to take the energy recovery pills, but Area 4 is dark and requires the flare bombs.

[edit] Walkthrough

After you land, walk right until it gets dark, then, hit start to launch the flare bomb and light up the level. Continue left until you reach the transmission room. Receive all transmissions and exit. Follow the level until you reach the door to the boss room and enter it. You don't have to kill the boss, just the core. Stand on the platform next to the core and fire, but be careful, the boss uses a grapple arm that will knock you off.