This article contains SPOILERS for Dragon Ball super #87
A classic Dragon Ball artifact was brought back to explain one of the biggest plot twists in Dragon Ball Super. Frieza's return in the manga came with the shocking revelation that he is now many times stronger than both Goku and Vegeta, and it's all thanks to something that Dragon Ball fans will instantly recognize: the Room of Spirit and Time.
Also known as Hyperbolic Time Chamber in the English translation, the Room of Spirit and Time was introduced in Dragon Ball Z. It is a mysterious, almost empty pocket dimension that can be accessed from Universe 7 via different doorways. The room has a time-compressed nature, which makes the flow of time faster than on the outside. Along with its increased gravity and reduced air thickness, this makes the Room of Spirit and Time the perfect environment for training, as a warrior is able to compress months or years of intensive training while only a few days pass in the outside world. Earth's protectors have used it often to become stronger, most notably during the Cell Saga and several times in Dragon Ball Super.
Variants of the Room of Spirit and time are known to exist in locations different from Earth and have different conditions. In Dragon Ball Super #87, by Toyotarou and Akira Toriyama, Frieza makes his glorious return. The galactic tyrant displays impressive power in his new Black Frieza form, first by effortlessly killing Gas, who was supposed to be the strongest warrior in the universe (after expressing a wish to the Dragon Balls), and then by taking out both Ultra Instinct Goku and Ultra Ego Vegeta with one blow. Frieza explains that, on one of his many conquered worlds, he happened to find a Room of Spirit and Time, where he trained for ten years, thus becoming the actual strongest in the universe (because when Gas expressed his wish, Frieza was technically outside the universe in another dimension).
The first Room of Spirit and Time on Earth had some strict limitations to its use, as no one was able to spend more than two years (two days in the outside world) inside, and it could only be accessed twice by the same person. After it was destroyed, the Namekian Dende rebuilt an improved version, removing the limit to the number of accesses and increasing the maximum permanence for each access to three years. The version that Frieza found, however, seems to be even more powerful, as he was able to train for ten years straight. Using a Room of Spirit and Time is also the perfect way to give Frieza a power-up. Due to his enormous natural talent, he never trained once in his life, before his first defeat at the hands of Goku. After that, he trained for just four months and obtained the powerful Golden Frieza form, which Goku and Vegeta were barely able to beat. It makes perfect sense, then, that ten years' worth of training would make Frieza the strongest in the universe.
Goku and his friends used the Room of Spirit and Time often to "cheat" and become stronger than their opponents in a short amount of time. It's a great twist, then that Dragon Ball Super shows a villain using the same trick, taking away one of the main advantages of the heroes, and proving that the series can still be very creative.