Get B rank on level 2
Get B rank on level 4
Unlock J.J. Sawyer:
Beat the game with an S rank in all levels.
Beat the game with an A rank in all levels.
Stunt attack mode:
Beat Story Mode.
Unlock Ethan costume C:
Beat Stunt Attack.
Unlock Kat costume C:
Beat Score attack:
Beat the game in Story mode, Score attack, and Stunt attack.
Always on Top of the Score List:
Choose New game and enter your name as Ethan and the PS2 will think you've completed the game.
Thanks to Revolution readers teie jansen and Simon&James!