Dragon Ball Daima Episode 20 finally revealed how Goku achieved Super Saiyan 4, but the explanation contradicts previous ...

He has had black, blonde ... Each form will be limited to one inclusion. For example, Kid Goku will cover all series that use that form. Oozaru will be omitted, just because Goku's Great Ape ...

which explains the nostalgic throwback to Goku being a kid again. Funnily enough, this will be the third time Goku has experienced childhood overall: he started out as a kid before he got de-aged ...