At the main menu, press Up, Up, Down, Down, Left, Right and you will have infinite Kelos.
When in the Persian Camp, you will be fighting a lot of people, so you can stack up on Kleos. When at Hydarnes, you will have to attack him with your spear. you should block, attack, block, and so forth. Only kill one immortal that attacks you, because he will call on more. When his shield is down, he runs to a cage. Go near one of the crucifixes and stand beside it. He will shoot his arm at you. Go behind the crucifix and he will get stuck. Go to the next one and do the same. Throw a spear at him when both arms are stuck. Rinse and repeat until he is dead.
Note: This code can only be used once.
25,000 Kleos Pause the game and press Down, Left, Down, Left, Up, Left.