Megaman X6 Codes -

X's Ultimate Armor:
Press at the title screen, then press (x3), at the main menu before starting a new game. A sound will confirm correct code entry. You will begin the game with X's Ultimate Armor.

Nightmare Zero:
Press at the title screen, then press (x3), at the main menu. A sound will confirm correct code entry. Start a new game. 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.

Zero:
Find Zero with the teleporters and fight him. He will join you after he is defeated.

Easy attack with Zero:
Press Attack and Dash continuously with Zero.

Nightmare effects:
Each effect is neutralized in almost in all cases by the same weapon it comes from. In the case of the raining magma, blow it up with ShouenZan or Magma Blade. For iced floors, use Hyoroga/Ice Burst. For gnats, use Yammark Option. For iron blocks, use Metal Anchor/Rakukojin. For soul spirits, use Laser Shield. Finally, red crates can be blown up with SentsuiZan/Ground Dash; black and blue ones can be moved with the same weapon. The rain and the spotlights cannot be neutralized.

Amazon Area, Laser Institute: Metallic gnats (very pesky)
Amazon Area, Magma Area: Metallic gnats
Inami Temple, Amazon Area: Normal rain (slows you down)
Inami Temple, Central Museum: Normal rain
Magma Area, North Pole Area: Magma rain. Also, some walls break an allow access to secret area.
Magma Area, Weapon Center: Magma rain.
Weapon Center, Amazon Area: Spotlights (dispiriting and very difficult to maneuver with)
Weapon Center, Inami Temple: Spotlights
Laser Institute, North Pole Area: Soul spirits (attacking soul clones of Zero/X, respectively)
Laser Institute, Inami Temple: Soul spirits
North Pole Area, Recycle Lab: Iced floors
Recycle Lab, Magma Area: Iron blocks
Recycle Lab, Weapon Center: Iron blocks
Recycle Lab, Central Museum: Iron blocks
Central Museum, Recycle Lab: Red, blue and black crates
Central Museum, Laser Institute: Red, blue and black crates

Defeating Bosses:

Commander Yammark: Ray Arrow
Ground Scaravich: Yammark
Blaze Hentnix: Ground Dash
Blizzard Wolfang: Magma Blade
Rainy Turtoid: Ice Burst
Metal Shark Player: Meteor Raiin
Shield Shelden: Metal Anchor
Infinity Mijinion: Guard Shell
Dynamo: Meteor Rain
High Max: Magma Blade
Gate Boss 1: Metal Anchor
High Max: Magma Blade
Gate: Invinsible Dash or Shadow Armor Giga Attack
Sigma 1: Metal Anchor
Sigma 2: Ground Dash