Instructions
Jump down off the side of the bridge after your first battle with Darth Vader at the Death Star to fight him again and get revenge. This is how you choose to be bad in the game. If you want to take the good route, you cross the bridge instead to kill Palpatine. Be aware that this fight is ultimately harder than the fight against Emperor Palpatine. This is because you can't recover any life during the much tougher fight with Vader.
Run toward Vader when attacking. If you jump toward him, he will grip you in mid-air and throw you away. Use "Force Grip" because Vader is not vulnerable to very many attacks. Wait until he is down to use any light-saber attacks against him. Alternatively, if you manage to get him down, you can use the opportunity to set up another attack.
Press the "Attack" button twice, followed by a "Force Lightning" attack and a "Force Push." Your character will perform an impressive three-move combo followed by a lift, which sends Vader into the air. If you've done it correctly, the third hit should electrify him, and the fourth should momentarily put him out of action. You must have the Sith Saber Slash and Saber Slam moves unlocked to be able to perform this combination.
Perform a "Force Grip" or a "Dashing Rush/Push" attack to get Vader onto the ground quickly after he has been lifted into the air. Speed is important because you need to capitalize on the opportunity to inflict some real damage. Rush into Vader and perform some combination attacks while he is on the ground.
Use ordinary attacks only when Vader is down on the ground or otherwise vulnerable. He is very resistant to most common attacks. Repeat the combinations in Steps 3 and 4 to get Vader down again. Attack him until he is finished off. You will receive the Sith ending to the game and the "Sith Stalker" costume for your evil efforts.