The Guardian Legend/Corridor 21

The new gate in Area 0
After defeating every boss and clearing every corridor in the game, a new corridor will appear in. You may have passed through this nondescript room before, but it will now be populated with a corridor gate. Head to location X9 Y11 to find the entrance to Corridor 21, the last corridor in the game. This will be your last chance to explore any part of the labyrinth, so before you hop in you may want to ensure that; you have a full meter of health, you have a full inventory of chips, and your favorite weapons are as strong as they can be. If you're prepared, then dive into the corridor and prepare to face a number of bosses back to back.

Corridor 21
This corridor could very well be considered a boss-rush stage. The only regular enemy that you will encounter are falling green asteroids. Other than that, all you will face is one boss after another. Only use your main guns on the asteroids, conserve your chips for the bosses.
 * Boss 1 - Fleepa:The first boss that you encounter is a blue Fleepa. While you have become considerably more powerful, this fishy boss has not.  As a result, don't be surprised when you destroy it with only two or three shots from a powerful weapon like the Fireball.  You can even stand to remain in front of it the entire time, and not sustain much damage.


 * Boss 2 - Zibzub:The next boss to face you is the Zibzub. Once again, you can remain directly below the boss as it bounces around the screen, and fire directly at it.  Use the Fireball or Repeller to maximum the amount of damage you do to it with each shot.


 * Boss 3 - Clawbot:A blue Clawbot comes next. Because this is the blue variety, it is considerably slower than the red one you face most recently.  Continue using the tactic of firing upward at it with the Fireball or Repeller until the lower portion drops off.  Then lead it to either side and shoot at it indirectly when the upper portion attempts to line up above you and blast you with its laser beam.


 * Boss 4 - Optomom:A red Optomom comes next. If your Fireball has been boosted to Level 3, there is no question that this should be your weapon of choice, since the Fireball can destroy the strands of seaweed that the Optomom releases.  No other weapon possesses this ability, and the Fireball will effectively destroy the Optomom's greatest defense.


 * Boss 5 - Grimgrin:The next fight is against a Grimgrin. Up until now, you've had a pretty easy time with the bosses, and you may feel a bit invulnerable, but this boss still has the potential to cause a lot of damage to the Guardian if you do not carefully time your approach beneath him.  No matter how strong you've become, you will want to tackle this boss with every bit of patience that you have in the past.


 * Boss 6 - Bombarder:Next up comes a red Bombarder. With a strong enough Saber Laser, you should be able to neutralize the threat of the missiles that it fires at you relatively quickly.  Wait for it to appear, and position yourself directly in front of the the Bombarder with the Saber Laser firing.  The missiles will be destroyed before they can spread outward, and you will likely receive an item capsule for your efforts.

At this point, you will escape from the corridor, and begin navigating through the exit from planet Naju. When you make it far enough away, the planet's self-destruct sequence will initiate, and Naju will explode. But you're not out of the woods yet. In the vacuum of space, you will now be flying through a field of red asteroids as you make your approach to the evil creature that nested inside of Naju and is now incredibly angry to have lost its home.

Final Boss
The very last boss of the game is certainly the toughest, but not the smartest. This large creature occupies a lot of space on the screen, which gives you very little room to safely maneuver. It has a variety of attack methods including small bubbles and missiles, but the single most dangerous attack that it has are its claws, which it randomly extends to the bottom of the screen and retracts. Under no circumstances should you ever leave the bottom of the screen, as that will unnecessarily expose you to more danger. You should also never let go of either fire button. There's little reason to use any weapon other than the Fireball, as it will do substantial damage to the boss as it passes through its head. It will take a very long time, but the boss will eventually change from blue to orange, indicating that you have done a great deal of damage to it. Further damage will result in the boss changing from orange to red. Whenever the boss' color changes, it attempts to increase the challenge by throwing more bubbles and missiles at you. While this can be effective if you don't use a good weapon to clear a path in front of you, it actually works to your advantage since more bubbles and missiles means more chances for item capsules to appear and restore any lost health. Focus all of your attack power on the eye of the boss, and do your best to dodge the claws whenever they reach down to the bottom of the screen. After the boss turns red, it will only be a matter of time before it is destroyed. If you succeed, you will be treated to the ending credits of the game. You will also receive a password for the challenging mode of the game. Congratulations.