Advanced:
You have to first beat the "Adept" World Tournament AND have AT LEAST 30-36 (I can't remember the exact number) characters unlocked.
Cell Games:
In Dragon Arena: Use a Level 20-30 Character, and after about 15 (or more) battles, Cell will "Suddenly Break In". If you beat him, the "Cell Games Tournament" will become unlocked. You will be able to find it located after the "Advanced World Tournament".
Death is but a door, Time is just a window,...I'll be Back!!!!!