Super Saiyan 4 Goku is Unlockable
in the First Budokai Game

This obviously makes very little sense. With the exception of the bonus character of Great Saiyaman, the game’s own story does not even reach into the Majin Boo arc of Dragon Ball Z, let alone introduce characters and transformations from Dragon Ball GT. The prevalence of this rumor seems to stem for a “method” for unlocking Super Saiyan 4 Goku actually making its way to the respective GameFAQs code page for some time.

Of course, no-one actually unlocked the transformation/character, because it is not in the game. The game is many years old, has been released on multiple platforms in multiple countries in multiple languages, and no-one has uncovered a Super Saiyan 4 Goku, or even any remnants of it ever having been considered or in early development for the game.