Warning! Spoilers ahead for Dragon Ball Super chapter 83!
Goku's father Bardock obviously undergoes a new transformation other than Super Saiyan in the latest chapter of Dragon Ball Super, but because manga are ubiquitously not drawn in color, it's impossible to know exactly which new form he's achieved. However, fans can speculate based on forgotten one-offs and how Super has recycled storylines from non-canon movies before.
Bardock has been somewhat of an enigma ever since he first debuted in the non-canon film Bardock: The Father of Goku. A three-chapter manga series called Dragon Ball: Episode of Bardock that takes place after the original movie added to the Saiyan's enigmatic persona. Rather than dying, the destruction of planet Vegeta thrusts him into the past where he eventually assumes the form of Super Saiyan. Since it was written and illustrated by Naho Ōishi, fans don't really consider this story canon, like the film that inspired it. But Dragon Ball creator and official mangaka Akira Toriyama seems to be justifying this particular plotline in the latest chapter of Super in some capacity. And it's possible that Bardock unlocks a version of a transformation that first debuted in the DBZ film Lord Slug.
Related: Dragon Ball Super Digs Deep Into the Series' Past, and it Should Go Deeper
In chapter 83 of Super, a flashback shows Bardock battling the villain Gas, who has been trading blows with Bardock's son Goku in the present day. After Gas unlocks his berserker-like form against Bardock that Goku himself still hasn't been able to overcome, Bardock holds his ground even after sustaining heavy damage. Bardock eventually undergoes a transformation that allows him to overcome his opponent, though, he, too, passes
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