One Punch Man chapter 165: Garou goes nuclear, steals Saitama's move and becomes absolute evil.
Garou's new abilities are potentially limitless, making him one with the universe itself. Garou is even able to copy Saitama's own power, making the two at least equally matched.
Garou is surprised that Saitama is unscathed even after taking a punch so hard head-on while Saitama reassures a shocked Tareo that Garou will not be able to scratch him.
Garou and Saitama punch each other, but take no damage. He'll be back.
Garou tried to remain calm and collected, but he was genuinely terrified of Saitama. He thought that he would be able to beat him. Additionally, he could see the sun since they were launched into space. He opened a portal to the sun and punched Saitama into the hyperspace gate.
As Garou was defeated by Saitama, "God" communicates with him through telepathy and offers him the power to defeat the Caped Baldy.
However, with the introduction of characters such as God, it will be interesting to see how strong the character is and whether or not Saitama will go all out against the mysterious entity. That being said, Saitama hasn't used his full power in any of the fights in One Punch Man.
More surprisingly, after transforming into his Cosmic Fear Mode under the influence of "God", Garou was even capable of taking many Serious Punches from Saitama before ultimately being defeated.
To sum things up, it would be unwise to assume Garou is as strong as Saitama because he was able to copy one of his moves. Given Saitama's endurance, it is unlikely that Garou's attacks would have either killed or inflicted much damage. If that were to happen, then Garou's strength would be comparable to Saitama's.
This showed that God gave Garou significant powers to defeat Saitama – an obstacle in his path. In chapter 165 of the One-Punch Man manga, Garou was able to display shocking powers even comparable to the eruptive level of a star explosion.
During their fight, Garou directly witnessed the overwhelming strength Saitama possessed, likening him to the embodiment of unfairness.
The character referred to as “God” in One-Punch man is an otherworldly being that appears to grant people power but at great cost. The well-drawn character has made its appearance in different chapters in the manga, puzzling fans on the true nature & goal of this being.
Over the course of the manga, Saitama's few glimpses of emotions were towards Genos, so it actually makes sense that his death is what forces him to finally get serious.
Immeasurable Strength: Saitama possesses an immeasurable amount strength and as a result is capable of destroying powerful monsters and villains with a single one punch (though this strength is not limited to punches).
It would be Saitama. Reason being in one episode in season 2 Saitama one hit Garou and Garou was unconscious. Garou did hit Saitama before but it did nothing. Saitama could just use serious punch and Garou would be died.
Immense Durability: Boros was shown to be amazingly resilient, to the point of being the first opponent of Saitama to survive after being hit directly by his normal punch, despite having his full power sealed by his armor.
It would be tough for Saitama to punch Beerus, seeing how this God was able to easily evade all of Goku's attacks even in his Super Saiyan form. Even when Goku becomes a Super Saiyan God, Beerus is able to defeat him after a mighty battle.
[ Still trying to do the math on how, the only thing to ever actually damage Saitama in the series is a cat scratching his face.
The only event that came close to becoming a God-level Disaster Threat was the meteor in the first season, which Saitama managed to stop easily. Otherwise, for now, it seems like the only God-level threat that the universe might face is from God himself, who has made himself known numerous times in the manga.
According to Saitama, he achieved immense strength by performing 100 push-ups, 100 squats, 100 sit-ups, and running 10 kilometers daily for about a year. Genos hears this and doubts the credibility of Saitama's explanations, suggesting that the routine isn't stressful.
Gravity is about 1/5th as strong as Earth's on Io, so with a mass of 89.3 x 10^21 kg (half of Io canceling out the one-handedness), Saitama at the time could probably effortlessly lift 16 quintillion tons on Earth.
At one point, the protagonist of One Punch Man even slapped himself. While he gave himself a huge red mark, he seemed mostly unaffected by it, which suggests that he could likely withstand his own punch as well.
Saitama might be powerful, but even his physical strength cannot match Goku's strength. It should also be noted how Goku's Ultra instinct essentially scared the gods of destruction. Whether they're in the One Punch Man or Dragon Ball universe, Goku would easily be able to kill Saitama without much effort.
Being a supernatural deity, Rimuru is immune to any kind of physical attack, so Saitama's punches are a no-go. Moreover, destroying his physical body won't kill him unless his core is destroyed, that is, his soul. Until Saitama uses some special magic spell, he cannot defeat Rimuru.