I need some cliff notes for that JJk episode lol idk wtf was going on
Megumi was going to get killed by the piece of shyt curse user with blonde hair (Haruta, the one who fought Nobara and got the shyt beat out of by Nanami), the only ace Fushiguro had in his sleeve was force the blonde fukker to be part of a ritual with the only one of the 10 shadows that has never been tamed: Mahoraga, knowing full well that the Shikigami was going to kill the curse user and kill Megumi as well.
So, what happens next:
1.- Sukuna realizes something is going on so he tells Uraume to keep waiting and get ready (we don't know for what yet). So he shows up, saves the blonde fukker and realizes that Megumi just kamikazed himself and unleashed Mahoraga. In order to stop Maho, Sukuna has to defeat it.
2.- Sukuna once again says he needs Megumi for something so he heals him up a little before going to battle.
3.- Sukuna vs Maho. It's basically 12 minutes of Sukuna using his "Cleave" technique on everyhing in his path in order to hurt and try to defeat Mahoraga. Because Maho is such a beast and "Cleave" adjust to the level it needs to cut the oppoent, all of Shibuya gets fukked up beyond recognition. You basically saw two tornados destroy that whole part of the city.
4.- As the fight continues, Sukuna begins to understand how Mahoraga works. It's a a Shikigame that adapts to all phenomena, so every time it got sliced up by an attack, it adapted and then the circle crown above its head moved, starting a new cycle with a Mahoraga with more knowledge and no injuries. Sukuna laughs because he realizes that's the technique Megumi wanted to unleash in season 1, which would've killed Sukuna with the amount of fingers he had back then.
5.- Once he realized what the fukk Maho was about, Sukuna unleashed his Domain Expansion, which is different from other DE (we get the full explanation in the anime). The surefire hit consists of a series of "Cleaves" and "Dismantles" (which fukk up non curse users) and a 140 meters radius (which Sukuna reduced from 200 meters so he wouldn't hurt Megumi).
6.- The attack defeats Mahoraga and also completely destroys everything in the 140 meter radius, including the people in it.
7.- Sensing he's about to lose control of Yuji's body, Sukuna leaves Megumi in front of Shoko, who has the ability to heal him up. And before he gives control back, Sukuna stands right in front of the destruction he created so he can torture Yuji by letting him see the devastation AND get the memories of everything Sukuna did while in control.
PS: We also get an explanations of Haruta's technique. Which basically stores small everyday "miracles" and releases them when his life is in danger in order to save him. It's explained those miracle had been drained in order to save him from Nanami's ass beating. So when Sukuna tells him to go away, he Cleaves him and dies.
PS2: When explaining Maho's power, we get a flashback of Gojo telling Megumi than hundreds of years ago, someone from the Gojo clan had the same techniques as him, and someone from the Zenin clan had Megumi's 10 shadows technique. When they fought each other, both died, implying that Fushiguro has the potential to be on THAT kind of level.