As the King of the Monsters, Godzilla is commonly depicted as the ultimate threat, besting even seemingly unbeatable foes in both Toho's movies and Legendary's Monsterverse. And in a sense, his atomic breath is emblematic of his prowess in battle; as his signature ability and the most commonly used tool in his arsenal, much of the damage Godzilla is able to wreak is owed to that power in particular. Needless to say, it's an incredibly potent destructive force, regardless of the specific canon in question.
Godzilla's atomic breath has been the cause of death of several major villains in the franchise, including Mothra, King Ghidorah, Kumonga, Megaguirus, and even the 1998 version of Godzilla. The Monsterverse has been consistent with its deadly reputation; even though Kong only took a glancing blow from the atomic breath, the deep hole it punched in the Hollow Earth made it abundantly clear that Kong only narrowly escaped death a few times in the movie.
However, none of this is to say that the atomic breath is unrivaled. Godzilla has gone up against some truly powerful adversaries, some of which are monsters who managed to push him to his limit. And oftentimes that's because his atomic breath ran into a brick wall. Hedorah, for instance, withstood his blasts in Godzilla vs. Hedorah.
Plus, other monsters have answered the atomic breath with incredibly dangerous beam attacks of their own. And it's also worth noting that certain versions of Godzilla himself has weapons at his disposal that are arguably greater threats than the atomic breath.
Every iteration of Mechagodzilla comes equipped with a strong ranged attack intended for fighting Godzilla. The 1990s version of the robotic kaiju, introduced in Godzilla vs. Mechagodzilla II, boasted the Mega Buster, a rainbow-colored beam attack it could emit from its mouth. It could stand up to Godzilla's atomic breath in battle, which was entirely by design. The humans needed Mechagodzilla to have a weapon that could counter Godzilla's signature power.
In that respect, the human characters got what they wanted, as evidenced by the scene where the atomic breath and the Mega Buster get locked in a beam clash. Neither monster won, with both ultimately falling over. The Mega Buster had proven to be an effective rival to the atomic breath, but it was not superior. The Mega Buster was so powerful that it drained Mechagodzilla's energy, more so than the atomic breath did to Godzilla.
The Mega Buster was designed to counter the atomic breath, but the humans had no response for the ability that Godzilla developed after absorbing energy from Rodan. Following his defeat at Mechagodzilla's hands in Godzilla vs. Mechagodzilla II, Rodan imparted what was left of his fiery essence to Godzilla, granting him a significant power-up, and a new abilty to boot.
Replacing his blue atomic breath was the red spiral heat ray. Stemming from the combined power of Godzilla and Rodan, the red spiral heat ray accomplished what the atomic breath couldn't; in the rematch, another beam clash ensued, this time with Godzilla's red spiral heat ray overwhelming Mechagodzilla's Mega Buster.
After the events of Godzilla vs. Mechagodzilla II, the red spiral heat ray served Godzilla extremely well, becoming an invaluable tool in his wins over SpaceGodzilla and Destoroyah.
In the next movie, Godzilla was faced with an attack much more threatening than the Mega Buster. For its titular villain, Godzilla vs. SpaceGodzilla introduced the Corona Beam, an orange beam blast composed of high levels of cosmic energy. Not only did it do great harm to Godzilla, but it was difficult to avoid. SpaceGodzilla could curve the blast, meaning he didn't have to strike in a straight line in the same way that Godzilla typically utilizes his atomic breath.
The Corona Beam's power level was on display when SpaceGodzilla used it to destroy one of Moguera's arms. Thanks in large part to the Corona Beam, SpaceGodzilla gained a clear advantage over Godzilla in battle. Only by destroying SpaceGodzilla's power source was Godzilla able to create a path to victory.
Godzilla had to go up against multiple powerful attacks when he encountered Destoroyah in the final installment of Heisei series, Godzilla vs. Destoroyah. Destoroyah possessed several weapons, with the two strongest being the Micro-Oxygen Beam and the Variable Slicer. The Micro-Oxygen Beam hurt Godzilla severely, but what was even harder for him to deal with was the Variable Slicer, the blade-shaped energy omitted from the horn on Destoroyah's head.
Godzilla has tremendous physical resilience, which is made clear by the beatings and blasts his body has taken over the years. But the laser horn actually cut into his body. Destoroyah came uncomfortably close to cutting Godzilla in half. The fact that Godzilla was in his strongest state (the Burning Form) says a lot about the potency of Destoroyah's Variable Slicer.
The most powerful ability that Godzilla has access to is the nuclear pulse. It has been a part of Godzilla's powerset across three different continuities. In both the Heisei and Milliennium eras of Godzilla history, the nuclear pulse acted as a defense mechanism, one that Godzilla would resort to when his mobility was restricted. When trapped by Biollante, he would respond by lashing out with a nuclear pulse, a blast of nuclear blue energy emitted from all sides of his body. A similar attack was used to kill Orga in Godzilla 2000.
In the Monsterverse, Godzilla: King of the Monsters took what was already a highly effective weapon and turned it into the strongest power in the entire Godzilla franchise. It pulled this off by merging with its take on Godzilla's Burning Form. The two turned out to be an overpowering combination; while in his Burning Form, Godzilla obliterated King Ghidorah - the second strongest Titan in the Monsterverse - with just three uses of his nuclear pulse.
The ability that has consistently plagued Godzilla the most in the franchise is none other than the gravity beam, the blast of yellow lightning employed by his archnemesis, King Ghidorah. But while it does damage to Godzilla, its power level doesn't quite match that of the atomic breath. After all, a big part of what drives its efficiency is the frequency in which Ghidorah uses it. It's the sheer volume of gravity beams Ghidorah hits him with that makes it a problem.
The same can't be said for Destroyed Thunder, the Godzilla: Final Wars equivalent of the gravity beams. At the end of Final Wars, the final boss of the movie, Monster X, transforms into "Keizer Ghidorah," a creature depicted as a much stronger relative to Godzilla's three-headed adversary. This version is more powerful than him in every way, and that extends to his gravity beams.
Whereas Godzilla can normally withstand the gravity beams for at least short lengths of time, he was quickly outmatched by Keizer Ghidorah and his Destroyed Thunder blasts. The strength of the ability goes hand-in-hand with the notion that Godzilla had encountered his strongest opponent ever.
