Get a 100% completion to have Lego Studs rain inside Barnett College.
Hidden Star Wars character locations 

  C3PO: Play the Raiders Of The Lost Ark: The Lost Temple level. Find the room 
  that is sealed off by metal Lego pieces. Use a bazooka or grenade in Free Play 
  mode to reach him.

  Chewbacca: Play the Raiders Of The Lost Ark: City Of Danger level. Reach the 
  last area of the mission where you change to a guard and get through the 
  checkpoint where the truck is stored. At the back of that area is a 
  hieroglyphic display. Have a Scholar character complete the puzzle. Go inside 
  the newly opened door to find the Mos Eisley cantina. Chewbacca is behind a 
  fence, and can be reached with a short character such as the Maharaja or Short 
  Round.

  Luke Skywalker: Play the Raiders Of The Lost Ark: Into The Mountains level. 
  Search inside the cave somewhere in the mountains. Use a bazooka or grenade in 
  Free Play mode to enter it.

  Princess Leia: Play the Temple Of Doom: Free The Slaves level. Go to the 
  second to last room. Go near the machinery on the far right-hand side of the 
  room, then walk toward the screen to find the way down to her.

  R2-D2: Play The Last Crusade: Desert Ambush level. When you start, go left, 
  and climb up the mountain to the gold chest. Once you get the chest, follow 
  the ledge to the left. You should see a brown whip point. Use Indy's whip to 
  pull down a tube from a Sandcrawler. R2-D2 will appear from it.