The ghost characters of Yoda, Anakin, and Obi Wan will become available for purchase to the player in the shop following the completion of all of the levels in the game.
You have to buy him for 2 million studs i think. You can also buy ghost Yoda and Anakin. Obi-wan,Yoda and Anakin sky-walker became force ghost;s but they weren't the only ones all the Jedi's became force ghosts.