Once you have completed the game, go back to mission #17, Revenge of the Sith. You will play as Anakin instead of Obi-Wan. If you defeat Obi-Wan you get to watch an alternate ending.
When in a duel select Ben Kenobi. In the duel press and hold block(L1), square and circle. He will bring his lightsaber up to his face like in episode IV. If you want to get killed you only have about a second to get hit. If you are hit the right way Ben will disappear (ala A New Hope).If you are hit a different way like a grapple you just die. It is really cool if you play in the death star arena and your opponent is Darth Vader
Several areas of the game require you to open a door and enter into an area, at which point you'll be attacked by enemies. In some of these places, if you're health and/or force energies are low and need to be given time to recharge, simply stand back past the doorway to the previous room. Most of the time, the enemies cannot pass the room they are in, and will stand huddled in the doorway.
Also, using Saber Throws (Or, later in the game, when Anakin aquires Force Lightning) you'll actually be able to get to these safe spots and kill the enemies that are standing just outside the doorway. This is especially helpful during missions like the "Assassination on Mustafar", where you'll constantly find yourself fighting Brutes, Guards, and Battle Droids.
Complete the listed Missions to unlock the listed Duel Arenas or Bonus Missions:
Beat the missions below to unlock the concept art