If you weren’t aware of Super Saiyan 4’s origin in Dragon Ball Daima, the finale reveals that Goku was able to achieve the level through off-screen training. While he first debuted the transformation ...

For example, Kid Goku will cover all series that use that form. Oozaru will be omitted, just because Goku's Great Ape form is not unique. Still, it is a simple but great design.