WARNING: The following contains spoilers for Dragon Ball Super Chapter 66, by Akira Toriyama, Toyotarou, Caleb Cook and Brandon Bovia, available now in English from Viz Media.
As a franchise, Dragon Ball Super has pushed Goku and his fellow Saiyans to new heights of power, unveiling transformations that have put them in competition with literal gods. While up until now Goku's most powerful form has been Ultra Instinct Perfected, Dragon Ball Super Chapter 66 seemingly unveils a brand new transformation for the Saiyan hero.
Due to Goku's hubris, the energy-absorbing Moro was able to gain access to the powers of the Angel Merus, whom he fought earlier in the arc. However, as a side-effect of his body not being prepared for divine power, Moro involuntarily merged with the Earth itself, putting Goku in the position of having to destroy his planet so as to save the galaxy.
In Dragon Ball Super Chapter 66, Moro's energy-absorbing abilities allow him to essentially drain anyone who touches the planet's surface. Hoping to still save Earth, Whis advises Goku to destroy the gem in which Moro is storing Merus' power so as to save everyone. Goku quickly goes on the offensive, but even Ultra Instinct Perfected and assist from Vegeta isn't quite enough to get him to Moro's gem. Soon, Goku ends up in Moro's grasp and his energy is drained, thus causing him to lose Ultra Instinct Perfected.
Seeing that Goku is losing the battle, Piccolo and Vegeta work with Z-Fighter allies across the planet to give their chi to his long-time rival. However, their mortal energy proves insufficient, and Goku is only able to access Super Saiyan Blue. Then, a massive boost of divine strength comes, which is revealed to be from Oob -- the reincarnation of Dragon Ball Z's Evil Boo.
Oob's power pushes Goku to new heights and he grows to a size reminiscent of his Great Ape form, though with a distinctly Super Saiyan transformation. This massive form wrestles with Moro, clearly overpowering the outmatched villain. Goku then spawns a miniature version of himself from his forehead that unleashes a devastating attack that destroys Moro's gem and seemingly kills the villain without wrecking the planet.
Overall, the ability boost Goku gets from this new form -- which is not named in the chapter -- seems to greatly surpass that of Ultra Instinct Perfected. That being said, the fact the energy required for this transformation came from Oob means Goku probably won't be able to readily access it again in the future. However, Goku has proven that, if there's a new power level to be obtained, he's going to do his best to get there, so permanently gaining this power could very well be the future of Dragon Ball Super.
Dragon Ball Super Chapter 67 releases Dec. 20.