100% Freeza?

[Let's Go Fearless!]

Why didn't he used it against SuperGoku when he was losing?

 

[Animelover5487]

He was, Freeza mastered his final form in Super so he probably wouldn't need to bulk up his muscles to use his full power.

 

[Let's Go Fearless!]

And yet couldn't master his golden form?

 

[Fantastische Hure]

Yeah, I thought it was obvious he mastered his true form.

Similar to you kind-of first master Super-Saiyan in-order to become Super-Saiyan 2 later.

 

[Papasmurf]

He did say that he'd never even tested his Golden Form before so he didn't know about the rapid stamina drain. He pretty much just attained the form and presumed it'd be invincible, altho to be fair if you'd only heard Galu had defeated Majin Boo you'd presume the same thing

 

[Spiral-Force]

He likely found a way to access his 4th forms' full power w/o larger muscles and stamina issues. The same can be said for GT Frieza.

 

[Tapion]

Since Super follows Z Fillers, and Freeza is shown trying to escape Hell more than once in those fillers, it's presumable that he mastered the form in the other world

 

[Jerk Store]

He probably mastered it during his training.

 

[Jeff Styles]

Probably master it like Goku and Gohan did with SSJ, not bulking up.