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, chosen for the Sea Area. This should be a warm-up fight.  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 technically don't need to use special weapons to get the job done.


 * Boss 2 - Zibzub:The next boss to face you is the Zibzub, which does not match the Area theme in order. Once again, you can remain directly below the boss as it bounces around the screen, and fire directly at it.  The Fireball or Repeller should maximum the amount of damage you do to it with each shot.


 * Boss 3 - Clawbot:A blue Clawbot comes next, chosen for the Jungle Area. Continue using the tactic of firing upward at it with the Fireball or Repeller for a balanced fight; Saber or Cutters to quickly kill the first part agressively, or use the laser for the safest fight 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, chosen for the Crystal Area. If your Fireball has been boosted to Level 2 or Level 3, there is no question that this should be your weapon of choice, since the Fireball is the only weapon that destroys the strands of seaweed that the Optomom releases.  Still remain cautious as the seaweed can still do a lot of damage.  This is the only Optomon fight that can generate power-ups because of the Asteroids.


 * Boss 5 - Grimgrin:The next fight is against a Grimgrin, chosen for the Alien Area. 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.  Use the same strategy with using the Level 3 Lasers.  If you want to make short work with the final part of this boss real fast (and recklessly expensive), use the Level 3 Seekers; just make sure to pick up the remains of the items.


 * Boss 6 - Bombarder:Next up comes a red Bombarder, chosen for the Wastelands Area. While this biss is very easy to beat, use this boss fight to replenish chips, health, and Enemy Erasers.  The bullet shield would be your safest bet as it is strong enough to dish out the missiles without worrying too much about accidentally touching the boss.  If you are precise enough, a well-timed shots with the Saber, Fireball, and Repeller right before the missiles blossom from the center of the boss will save you more chips.

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
If you did not conserved enough chips and Enemy Erasers from the Bombarder fight, you are in for a real hurt. The very last boss of the game, known as "It" 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. The bubbles and missiles take a while to destroy, with only a few weapons that can destroy it effectively. It also inflicts a lot of damage when not being careful.

At this rate, all of your weapons should be upgraded to its maximum power. Take a look at the strategies:
 * Side Waves: Use this ONLY when going behind the boss. There is a small gap where the boss can't touch you.  Make sure you have a LOT of chips to use and spam this to ensure that the repeated use of the side beams hit the boss and destroy the missiles.  With this method, you don't have to worry about the claws.
 * Seekers: This is the most aggressive and fastest way to defeat the boss. This method gives you the most freedom of movement.  It has a good chance of eating the missiles and bubbles, but always be careful when the seekers miss it.  If the seekers miss it, you are left very vulnerable to destroying the missiles with your regular gun.
 * Fireball: The most basic way of defeating this boss. Spam this and with precise timing.  You need to keep spamming this to reduce the impact of the missiles and bubbles heading towards you.  If you use the fireball, you have to face this boss regularly.
 * Repeller: Use this weapon on the edges of the screen and remain next to the repeller's shot to have the homing missiles get knocked out from the repeller. Dodge precisely.
 * Grenades: Take critical aim when using grenades. They are show, but very precise timing will take out a good amount of homing missiles for a short duration per shot.  Do NOT miss!
 * Cutter: Stay a certain distance from the boss; not too close nor too far. Too close would mean taking severe contact damage and the missiles won't get hit.  Too far and you won't hit the boss and the missiles will hit you from behind directly.

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, which increases in speed and how much can be shown on-screen. While it actually works to your advantage since more bubbles and missiles means more chances for item capsules to appear and restore any lost health, don't overrely on it too heavily. 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.