Unlock X's Ultimate Armor:
Press Left(3), Right at the Main menu before starting a new game and if the code has been entered correctly you will hear a sound as confirmation.

Unlock Zero:
Use the teleporters to find Zero and then fight him. When you have defeated him he will join you.

Unlock Nightmare Zero:
Press L1(3), R2 at the Main menu and if the code has been entered correctly you will hear a sound as confirmation. Start a new game and when you rescue Zero after defeating him in battle you will play as the Nightmare version of Zero. Nightmare Zero has ALL of Zero's normal moves but he is much more powerful.


Boss Weaknesses
The following is a list of each of the bosses and their weakness.

Rainy Turtoid - Ice Burst

Dynamo - Meteor Rain

High Max - Magma Blade

Gate Boss 1 - Metal Anchor

High Max - Magma Blade

Ground Scaravich - Yammark

Blaze Hentnix - Ground Dash

Blizzard Wolfang - Magma Blade

Commander Yammark - Ray Arrow

Gate - Invinsible Dash or Shadow Armor Giga Attack

Metal Shark Player - Meteor Raiin

Shield Shelden - Metal Anchor

Infinity Mijinion - Guard Shell

Sigma 1 - Metal Anchor

Sigma 2 - Ground Dash