Dragon Ball Z: Buu's Fury / Dragon Ball GT: Transformation

During the World Tournament Saga, after Videl's fight, Gohan asks Goku to get a Senzu Bean from Korin's Tower and get a bean from Yajirobe. When you get the Senzu Bean, eat it. When you go back Goku will still give Gohan a Senzu and when you look in your invintory, you will see that you have 255 senzu beans.

While performing the Fusion Dance, hit these buttons to complete a Perfect Fusion every time.

To unlock the Fusion Dance for Goku and Vegeta, you must collect all of the Z Exhibits and Hercule Exhibits and return them to their places. Once all Exhibits are returned, the man at the counter that takes up the Exhibits will tell you that you can use the Fusion Dance with Goku and Vegeta!

Most of these modes and characters can be purchased in the 'Secrets' section of the main menu. But the Single Player Mode has to be unlocked by completing the Story Mode.