Dragon Ball Super has added tons of new forms and attacks to the venerable shonen franchise, most notably the Super Saiyan God transformation. Also introduced in the series is the Ultra Instinct, a status of effortless control of one's body during a fight. Goku can eventually take on both of this transformation's forms, though it's an incredibly taxing experience. The technique is so advanced and specific that even Vegeta is unable to learn it.
Despite how long it takes for Goku to get the hang of Ultra Instinct, Master Roshi -- his old teacher -- showcases that he already understands its basics, though his unofficial version is both similar and different to his ex-pupil's.
Goku's Ultra Instinct
Goku's variation of the Ultra Instinct form and technique begins with the Ultra Instinct Sign phase. This form gives Goku a blue/silver aura that surrounds him and beams upward. It's first achieved by Goku casting off his physical limits and digging into his deepest potential. In the manga, this was done by resisting a powerful attack, while the anime version of Goku achieved this form as the culmination of all of his martial arts training. As powerful as this was, however, this Ultra Instinct Sign phase was still an incomplete transformation.
The complete transformation is the Autonomous Ultra Instinct, enabling the user to deploy any part of their body independent from the rest of their body's movement. By removing the need to think about attacks, the body can respond in nanoseconds to an opponent's moves. However, Goku has to completely clear his mental state and cast off all limitations to get to this level. Though initially done through the most harrowing of circumstances, this method caused sufficient stress on Goku's body. However, after seeing Merus' sacrifice, he gains the power to turn into the form at will.
Master Roshi's Ultra Instinct
As Whis is the one who taught Ultra Instinct to Goku, and Angels are described as naturally being in the state, he's far from the only character in the series to use the power. Beerus also uses the technique against the other Gods of Destruction. Surprisingly, however, it was a human character who also had his own take on Ultra Instinct. This was none other than Master Roshi, Goku's childhood teacher.
During the Tournament of Power arc of Dragon Ball Super, Goku temporarily finds himself unable to move past his physical limitations. Not only is Jiren unimpressed with the Saiyan, but so is Master Roshi, as he feels that Goku has come to rely on physical strength too much when he fights. Roshi then challenges Jiren himself, which the latter takes as a joke. However, the battle doesn't quite go as Jiren expects, as Roshi can easily dodge many of Jiren's attacks. Even though he's eventually defeated via ring out, Roshi's performance is impressive to many in the fight's audience, including Whis and Beerus.
They note that Roshi's ability to effortlessly dodge attacks automatically without thinking is eerily similar to the Ultra Instinct. This amateur take on the technique could be chalked up to Roshi's age and mastery of martial arts, as he's logically been training his body for far longer than Goku. Whis then stated that Roshi was the closest mortal ever to mastering the Ultra Instinct state, even if he didn't even know about it. It's only due to this ignorance of the Ultra Instinct and his lack of officially being trained in it that keeps Roshi from mastering it. Still, his evident knowledge of the technique's basics put him in a league above many of the franchise's fighters, including Goku himself.
