Vader is involved in the Imperial Themepark quest at the Emperor's Retreat on Naboo, where he may be found at any time. He may be visited only after completing missions for all the other NPCs in the themepark, including the Emperor. Darth Vader is the final NPC in this quest, and awards the Imperial Badge of Merit for completion of the themepark.
Lord Vader also appears in the heroic instance: Battle of Echo Base, where he is attackable. He is a CL 300 Boss and is located in the main hangar where the snowspeeders are normally at. He is impossible to kill as his HP bar does not drop when hit, regardless of the amount of damage.