One of the most iconic features within Akira Toriyama's beloved manga/anime franchise Dragon Ball is that its main characters from the alien Saiyan race are able to transform into a boosted combat form known as Super Saiyan. Over the years, progressively more powerful Super Saiyan forms have been unlocked, and by Dragon Ball Super, Goku and Vegeta become able to blend their Super Saiyan abilities with divine power into a form known as Super Saiyan God—which is immediately rebranded as Super Saiyan Blue for the blue hair and energy aura it emits.
However, the concept of Super Saiyans was expanded upon in Super in different ways, with one reimagining linked to a specific, fan-favorite antagonist: Broly. Featured in a trilogy of non-canonical anime films and video game adaptations, Broly could transform into a special brand of Super Saiyan: the mythical Legendary Super Saiyan that would appear once every thousand years, capable of wiping out entire worlds single-handedly. The latest anime film, Dragon Ball Super: Broly, officially introduced Broly into the mythos, while the anime series' Tournament of Power storyline presents a twist on the Legendary Super Saiyan concept through the Universe 6 Saiyan warrior Kale. However, how does a Super Saiyan God fare against the Legendary Super Saiyan?
In its original incarnation during the Dragon Ball Z era, the Legendary Super Saiyan form easily overpowers base Super Saiyans, but an adult Gohan is able to actually visibly stop Broly in his tracks on a couple of occasions at Super Saiyan 2. An offhand comment by Goku at the end of the subsequent film Bio-Broly indicates that Goku has repeatedly stopped Broly from causing trouble in Hell, unfazed by Broly's latest outburst—at this point in the series, Goku is able to transform into Super Saiyan 3 but notes that only Majin Buu and Janemba have driven him that far in battle before.
With Super Saiyan God and Super Saiyan Blue both far more powerful than Super Saiyan 3, this means they should be far stronger than the Legendary Super Saiyan form, but the canonical introduction of the mythical transformation in Super makes it significantly more powerful than the version seen in Z. Kale's Legendary Super Saiyan form forces Goku to transform into Super Saiyan 3, and Kale even fights on par with Goku's Super Saiyan God form before Goku begins to take the fight more seriously and outmatches her. Kale's transformation in the manga is more uncontrollable, though Vegeta and Cabba separately note that she is consuming her power too quickly to sustain it for long.
The canonical version of Broly introduced in Super steadily grows in power as he fights, initially fighting against Vegeta in his base state before forcing him to transform into Super Saiyan and Super Saiyan God. As Vegeta transforms into continually more powerful forms, Broly's combat strength rises to match and overpower it, with Goku similarly being outmatched at Super Saiyan God during his own bout against Broly. After Frieza murders Broly's father, an enraged Broly makes his full transformation into a Legendary Super Saiyan, easily overpowering Goku and Vegeta's combined efforts at Super Saiyan Blue and forcing them to fuse together into the composite Super Saiyan Blue warrior Gogeta.
This seems to prove that the version of Legendary Super Saiyan seen in Super is actually far more powerful than a standard Super Saiyan Blue, with only a fused Saiyan warrior able to keep up with Broly in that state. With Goku unable to achieve his Ultra Instinct transformation after the Tournament of Power, it is unknown how the most powerful Saiyan transformation seen yet could fare against Broly's Legendary Super Saiyan transformation, but the fight would certainly be a showdown to remember.