In Goku's First encounter with Jiren, Jiren matched a Kaiokenx20 Super Saiyan Blue Spirit Bomb, and Supreme Kai stated that Jiren's power feels different from anyone they ever faced before, meaning that Jiren is the strongest enemy they have ever faced. So, Jiren is stronger than Merged Zamasu.
Jiren is strong , super - strong , no doubt. But no matter what you say , he wont be more powerful than Fused Zamasu.
While Goku Black was able to overpower Super Saiyan Blue Vegeta, it still turns into a close fight. This means that Jiren would be able to outclass Goku Black by quite a bit. Jiren takes on Ultra Instinct Goku, which goes far beyond Super Saiyan Blue power.
While Goku and Jiren were relatively evenly matched during the Tournament of Power, and once MUI came into play, Goku will eventually beat Jiren with ease.
Broly is both the better character and the one who would win because Fused Zamasu was defeated by Super Saiyan 2 Trunks while Broly fought Super Saiyan Blue Gogeta. Its basically Super Saiyan 2 just ramped up to match Super Saiyan Blue.
Even though he's immortal, he's not invincible, he can be damaged - meaning Frieza could very well just wear down Zamasu's stamina and torture him for a while, before leaving him brutally beaten or something.
The only known way to beat Infinite Zamasu is to blow up the multiverse, which SSB Vegito can't. Even if Vegito could theoretically overpower some of the Zamasu heads, there's too much of Zamasu and Vegito would time out and defuse eventually.
Beerus was afraid Beerus would cause Xeno to destroy his universe, not of Jiren himself. He was scared Goku would lose.
Jiren manages to overcome the Spirit Bomb, but Goku emerges in a new transformation, Ultra Instinct. In this new state, Goku is able to fight Jiren more effectively and surprise him for a few moments before the forms gives out, allowing Jiren to defeat him again.
3 Can't Defeat: Jiren
Jiren was able to fight against Mastered Ultra Instinct Goku during the Tournament of Power, and he even held his own against him, meaning he should be able to do the same against Gogeta.
But without Ultra Instinct, Jiren still has the advantage over Goku. In order to defeat Jiren, Goku had to team up with both Frieza and Android 17. On his own, the only hope Goku has of defeating Jiren is by fully mastering Ultra Instinct, and being able to activate it at will.
While he had lost everything, Jiren does not become evil and instead becomes an overall selfless and heroic, but distant and cold. Possessing a powerful sense of justice, Jiren devotes everything in justice and never acts for selfish reasons.
Trunks then gains power from every remaining living thing on Earth, generating a Spirit Bomb that he channels into his sword to slice Fused Zamasu in half, destroying his body.
Later, Super Saiyan Blue Goku manages to hold his own against Fused Zamasu in one on one (though Fused Zamasu has a large advantage) and even blasts a hole through Fused Zamasu with a God Kamehameha, however, the fusion simply regenerated and takes down Goku by hitting him with many blocks of Katchin.
Immortality. Zamasu's immortal body. According to Zamasu, at some point in the future, he used the Super Dragon Balls to wish for a immortal body, which allows him to be unaffected by ki attacks, as he remained unharmed after taking the full brunt of Trunks' Final Flash and Black's Kamehameha.
Jiren is the only mortal being to be above a God of destruction, meaning it is almost impossible for the Hakai to affect him.
Jiren turns out to be one of the final opponents and he's able to give Golden Frieza and even Goku in his Ultra Instinct form difficulty. If these combinations aren't strong enough to defeat Jiren then Kale isn't going to accomplish it either, even in her Berserk form.
1) Beerus. Beerus is the God of Destruction hailing from Universe 7. He is the strongest God of Destruction among the 12 universes in Dragon Ball.
Monaka was initially described as being a hero of his home world planet, Wagashi. At some point in his past, he was said to have fought against the God of Destruction Beerus. He managed to cause Beerus trouble, which makes him later claim Monaka as the strongest fighter he's ever faced.
While he has no real love for his family, he is proud of his clan and respected his father during his lifetime, as he took his father's warning about never opposing either Beerus or Majin Buu seriously.
Lord Beerus is a Destroyer God who has the power to eliminate planets without breaking a sweat and can even collapse the entire universe if he's fighting at full strength. Beerus' power is incalculable, therefore Frieza wouldn't stand a chance against him.
The manga speculated that Vegito separated because Goku was stronger than Vegeta, resulting in an unbalanced Fusion, but the end result is the same: Vegito's time limit is his biggest weakness.
Goku may never pass Zeno and 4 other Dragon Ball characters
While his fight with Moro showed he can beat another Ultra Instinct user, Whis' Angelic heritage and proficiency is unfathomable.
Future Zeno, alongside Present Zeno, are among the most powerful beings in the entire Dragon Ball franchise. He is able to erase anything from existence, as seen when he erased Infinite Zamasu, along with all the future timeline's universes and the entire future timeline.