Dragon Ball Theory: The Series' Strongest Saiyan Could Unleash A Forbidden Form
Canon is a funny thing when it comes to the legacy of "Dragon Ball." For instance, though there have been 21 different movies in the franchise, only a few of them are considered to be official canon. Even more complicated is the history of Broly (Bin Shamada/Vic Mignogna), a character who, despite having multiple appearances over the franchise's 30-plus years of existence, has only been a part of the official timeline since 2018.
However, now that Broly is a part of "Dragon Ball Super," he may be bringing back another element of the series that has been scrubbed from canon. In the much-derided "Dragon Ball GT," a fourth version of the Super Saiyan power up was unlocked by Goku (Masako Nozawa/Sean Schemmel) and Vegeta (Ryo Horikawa/Christopher Sabat), which gave the Saiyans uncharacteristically long hair and a tail on top of heightened powers.
Since it is explained that Broly's power in "Dragon Ball Super: Broly" comes from the wildness and savagery of the Great Ape, and his appearance changes in accordance with this in the film, it seems that there is now an official version of the Super Saiyan that could theoretically lead to the form appearing in the current series.
If the form comes back, Broly would be the perfect Saiyan to use it
The clearest indication that Broly's powers are tied to the Super Saiyan 4 form in "Dragon Ball Super: Broly" is that his final powered-up form in the movie has him sporting golden pupils. Fans who watch "Dragon Ball GT" or have some experience with the other non-canon outings of the franchise will recognize immediately that this characteristic is unique to that form.
However, the fact that we still haven't seen the emergence of Super Saiyan 4 in the five years that have elapsed since "Dragon Ball Super: Broly" was released suggests that the creative team behind the series may be hesitant to bring back the form. Furthermore, the emergence of seemingly more powerful variants like Super Saiyan Blue and Ultra Instinct could suggest that the form has been rendered superfluous.
Even with this in mind, it's still possible that "Dragon Ball Super" could still bring back the form, if only as an exclusive transformation designated specifically for Broly. This would allow for the best of both worlds, where the form could return for fans of the design and mythology behind it without mucking up the continuity of the current series.