Fallen paladins:
You can make your paladins fall from grace and become necromantic with their power (turning instead or rebuking and vice versa).
Multi-player battles:
You can use one UMD for two separate PSPs to have multi-player battles.
Easy experience:
To easily gain experience,
When you finish killing all the monsters and NPCs in a mission, try to exit through another door than the one that triggers the end of the mission. This will end the mission without canceling the experience points. When you go back to the campaign map, the mission will still active and repeatable. Never level up more than the required level for the mission or you will not receive the experience for the specific level monsters. This is based on the fact that wizard made the game exactly off the core rulebooks of AD