In Infamous 2 for the PS3, there are a lot of powers you don’t have access to while you’re playing through your good/evil character since most powers require your karma to be at a certain point. There is a way to have access to all powers in the game however, which makes the post game a little more interesting.
To unlock all powers in the game, you need to play through the game two times, once choosing the hero route and once choosing the infamous route. Once you beat the game the second time, watch the credits roll and a message will pop up stating that you have unlocked all powers, and it gives you 15,000 xp to purchase the opposite powers of the karma you currently have selected.
Now you can go around town saving people or creating havoc to your hearts desire.