My guess would be that it's either Yoda or Vader, whichever didn't come standard with your system. They will be a purchasable download from XboxLive or PS Network.
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And for some reason it took us forever to beat Algol with Vader in the last part of the arcade mode last night XD It was worth it getting the Apprentice unlocked though.
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And for some reason it took us forever to beat Algol with Vader in the last part of the arcade mode last night XD It was worth it getting the Apprentice unlocked though.