Play NES Metroid
     To  pay the original NES classic on your GameCube, you must first
have  Metroid Fusion for GBA in addition to your copy of Metroid Prime
for GameCube. After beating Metroid Fusion, connect the GBA (while the
Fusion  cartridge  is in it) to the GameCube using the GBA link cable.
You  will  now  be able to play the NES version of Metroid and save on
the GameCube's Memory Card.

Unlock Metroid Fusion Suit
     To  do  this,  you  must have a copy of Metroid Fusion for GBA in
addition  to  your  copy  of Metroid Prime for GameCube. After beating
Metroid  Prime,  connect the GBA (while the Fusion cartrdige is in it)
to  the GameCube usign the GBA link cable. The Fusion suit will now be
available in Prime's File menu.