A great spin on the Super Saiyan transformation came all the way back in the Dragon Ball Z movies before Dragon Ball Super made this appearance canon by introducing Kale and retconning Broly's character, making the latter's motivations better for everyone to see. Given that this character is going to play a major role in the upcoming movie as well, here is everything that makes this Legendary Super Saiyan form so unique.
The most obvious and unique change brought about by the legendary Super Saiyan transformation is the manner in which it changes the aura and hair color of its user. The regular Super Saiyan transformation gives users a yellow aura and golden-blond hair, which has become synonymous with this epic transformation.
However, in the case of the Legendary Super Saiyan, users actually get greenish hair and a green aura as well. It's a small but noticeable change that shows just how different this transformation really is.
Before the advent of gentler Saiyan souls like Goku, there was a time when many people considered Saiyans to be nothing more than a ruthless warrior race that strived for death and destruction above everything else. While people might argue that their heinous actions arose as a result of Frieza's diabolical reign as emperor, that doesn't take away from the sheer depravity and brutality of the actions perpetrated by this race during their so-called conquest of the universe.
The term Legendary Super Saiyan is probably coined as a homage to the Saiyans of old, who thirsted for battle and destruction, leaving a wave of chaos wherever they went. Given how users lose their sense of reasoning and become monsters in this form, it's easy to see why this is the case.
A rather unique fact pointed out by Vegeta relates to the frequency of the Legendary Super Saiyan transformation, which is slated to appear once every 1000 years. It's a pretty unique fact that shows just how rare and powerful this transformation really is, although there's one particular detail that rubs fans the wrong way.
After all, it was Vegeta himself that stated that the last Super Saiyan was seen 1000 years ago, which can definitely throw a wrench in this statement. However, the manner in which Vegeta worded this statement should be looked at — he only said that the last Super Saiyan appeared 1000 years ago, and never outright stated that this was the frequency of their appearance. That statement was reserved for the Legendary Super Saiyan transformation instead.
Another interesting tidbit that Vegeta let the audience know about is that the Legendary Super Saiyan is possible the true form of this patented Saiyan transformation indeed, which is pretty interesting. It indicates that the regular Super Saiyan transformation is flawed from the get-go, which might indicate why it has so many different forms with varying degrees of power.
Meanwhile, the Legendary Super Saiyan form seems to be pretty sufficient at the peak of its transformative heights. There are no updated forms to be seen here, with Broly and Kale seemingly having a mastered version of the form from the get-go... although most people won't be surprised if Dragon Ball Super decides to retcon this aspect of the Legendary Super Saiyan transformation as well.
The Legendary Super Saiyan sends its users into a berserk state... that is unless they manage to master this form. It seems that this state is mainly caused due to the massive inflow of power experienced by a user, and this flow of power is apparently limitless.
This means that a person using the Legendary Super Saiyan transformation will never run out of either power or stamina, which can make them extremely tough enemies to deal with. These fighters need to be pummeled into submission for the form to be rendered ineffective, which can take some serious fighting chops indeed.