How do you unlock aliens in Ben 10 ultimate alien cosmic destruction ps2?

In Cosmic Destruction, you already unlocked all the aliens. You need to choose them first then you can play as the selected aliens. For Bonus aliens to unlock, go into the cheat section and type in the codes, Primus and Classic to unlock Fourarms and Rath. However them and the given aliens (Swampfire, Humungosaur, Ultimate Echo Echo, Ultimate Spidermonkey, NRG, Water Hazard and etc) are the only aliens that are playable in the game.