Sonic's Secrets: Bio-Hazard Battle.

On the title screen (see right), press and:

HOLD C and make a full clockwise circular motion with the D-pad, starting and ending in the Up position.

You should hear a noise confirming that the cheat has worked. When you start a game you will now be able to select which level to play (see right).

To both play as the same ship in a 2 Player game, highlight the 2 PLAYER option, then:

HOLD Right and press Start.
Don't release the Right button until the ship selection screen appears.

If your timing was right, both players will have the upper-right ship selected.