Hold Start + B + X for two to three seconds during game play.
Classic Metroid game:
Note: This trick requires Metroid Fusion and the Game Boy Advance and a link cable. Successfully complete Metroid Fusion and save the game. Connect both games with the link cable to unlock the classic NES version of Metroid.
To unlock the classic Metroid (via a link cable,Game Boy Advance, Metroid Fusion and completed Metroid Prime data), press Z at the main menu to highlight "Password", then enter JUSTIN BAILEY
Metroid Fusion costume:
Note: This trick requires Metroid Fusion and the Game Boy Advance and a link cable. Successfully complete Metroid Prime and save the game. Connect both games with the link cable to unlock Samus' Metroid Fusion costume.
Image Gallery 1 option:
Complete 50% of the research and creature data scans.
Image Gallery 2 option:
Complete 100% of the research and creature data scans.
Image Gallery 3 option:
Successfully complete the game under the hard difficulty setting.
Image Gallery 4 option:
Find 100% of all power-ups. Note: This does not include the Log Book.
Note: The last picture in this gallery is that of Samus without her suit in 3D.
Hard mode:
Successfully complete the game to unlock hard mode.
Alternate ending sequences:
Finish the game with a 74% or less completion percentage for the normal ending sequence. Finish the game with a 75% to 99% completion percentage to view an alternate ending sequence. Finish the game with a 100% completion percentage to view the best ending sequence.