If your referring to the Xbox 360 version.... You don't "unlock" him you download the content for him...
you have yo by him from the Xbox 360 live store that is the only way to unlock him.
if your talking about the playstation 3 version then you cant unlock him unless you buy him for playstation store but yoda is only available for the XBOX 360. same thing for Darth vador you cant unlock vador for 360 unless you buy him but Darth vador is only available on the PS3.
Download a mod which is only for PC version search it up on google: Darth Vader Skin or Darth Vader Mod Kotor 2
press a 500 times at start screen You start out with Darth Vader for the PS3 and with Yoda for the Xbox 360.
you cant vader=ps3 yoda=360
you have to complete arcade mode with yoda on xbox 360. Or you complete arcade with Darth Vader on PS3.
Darth Vader
Darth Vader
Definitely Darth Vader
Darth Vader
In the Family Guy version of Star Wars, Darth Vader is played by Stewie, who is an infant and doesn't have a "job."