Supreme Kai: Use Gohan's Dragon Universe for AT LEAST the second time. After you have unlocked Videl, AND beat Goten, go to Kami's lookout and beat Piccolo. When the Dabura fight appears, go to the mountain area of the main continent. Find the scene with Vegeta, and then go fight Dabura. After the Dabura battle, Gohan will now go after Vegeta instead of Buu. Beat Vegeta, and head towards the red dot. BEFORE you fight Buu, use the "Sense Aura" (R1) to find the "plains" spot near Central City. After the scene with Supreme Kai, he will become unlocked.
Death is but a door, Time is just a window,...I'll be Back!!!!!