The King of the Monsters didn't get to be the King without assembling a robust cast of villain monsters who have, at various points throughout the decades, attempted to bring his rise to the top of the kaiju food chain to a stop. Some of these rivals, like Baragon and Angurus, have failed to ever put up much of a fight.
Don't be fooled though, there are plenty of monsters who have given Godzilla a run for his money in the past. Among the most famous of which is the menacing Mechagodzilla; a robotic doppelgänger who has been constructed by either aliens or humans (depending on which movie he's in) to defeat Godzilla. One of the reasons why Mechagodzilla has posed such a threat in the past is his vast assortment of weapons and abilities (which vary across versions of the robot) that it can apply to lethal effect.
Missiles
One of Mecha G's most iconic abilities is its ability to fire destructive missiles from its fingers, or perhaps it would be more accurate to say that its fingers themselves are missiles waiting to be launched. In the Showa Mechagodzilla films of the '70s, Mechagodzilla would frequently use these missiles as weapons to engage opponents at range or to inflict destruction on cities.
Why exactly the aliens of Black Hole Planet 3 elected to place Mechagodzilla's missile launchers on its fingers is something of a mystery. Given their advanced technology, could they not have just mounted missile launchers on their shoulders instead? How's Mechagodzilla supposed to pick things up once it's fired all of its missiles?
Flight
With the notable exception of Mechagodzilla's newest appearance in Godzilla vs. Kong, nearly every iteration of the mechanical titan has had access to some form of flight capabilities. Flight affords a tactical advantage for obvious reasons, but the ability is especially helpful to Mechagodzilla given his wide array of ranged attacks.
In the original 1974 Mechagodzilla movie, Godzilla was left essentially at the mercy of Mechagodzilla's aerial attacks. Everyone's favorite giant lizard has always had something of a complicated relationship with flying, so he was only able to counterattack from the ground with his atomic breath, to little effect.
Defense Neo Barrier
Mechagodzilla's offensive capabilities are enough to make it a formidable anti-kaiju weapon, strong enough to go toe-to-toe with Godzilla himself, but no giant fighting robot is complete without robust defensive abilities as well. One of these is the aptly named "Defense Neo Barrier," a sort of energy shield that Mechagodzilla can generate by rapidly spinning its head.
In Godzilla and Mechagodzilla's inaugural confrontation, Godzilla was shown to have great difficulty penetrating the force field. Although Mechagodzilla appeared to be immobilized while using the shield, Godzilla's physical attacks and atomic breath were not enough to break down the defense.
Cross Attack Beam
One of Mechagodzilla's many ranged energy weapons is the iconic "Cross Attack Beam," a sort of projected energy beam that Mechagodzilla is able to fire from a hatch located in its chest. This beam is clearly a potent attack, as in 1974's Godzilla vs. Mechagodzilla, viewers can see it inflicting serious damage on Godzilla, as well as slicing through a cliff.
It's fairly typical of giant robots in Japanese media to be able to fire beams from their chests, so it's good to see that Mechagodzilla isn't an exception to this rule. This ability is common across many different iterations of Mechagodzilla, albeit with different names and appearances from movie to movie.
Space Beams
One of Mechagodzilla's signature powers is the ability to project twin lasers from weapons mounted in its eyes, referred to in the original vs. Mechagodzilla movie as space beams. These lasers appear to have a significantly faster fire rate than Godzilla's atomic breath, making them the ideal weapon to engage him with.
While perhaps not as strong as some of Mechagodzilla's other beam weapons, the Space Beams are no pushover when it comes to destructive power. In the past, they've been shown to successfully clash with Godzilla's atomic breath and to inflict serious damage when they find their target.
Mega Buster
Later iterations of Mechagodzilla have been known to change up its armaments. In 1993's Godzilla vs. Mechagodzilla II, Mechagodzilla is a human-built anti-Godzilla weapon, with some new abilities to make it more effective in combat.
Among the most notable of the new inclusions is the Mega Buster (not to be confused with Mega Man's iconic weapon), yet another ranged beam attack, but this time it's similar in functionality to Godzilla's atomic breath; being fired from the mouth of the machine rather than the chest or eyes.
Shock Anchors
Another of Mechagodzilla's newer weapons are the "Shock Anchors," which function essentially like kaiju-sized tasers, having been shown to deliver enough of a shock to incapacitate even Godzilla. These weapons worked by launching enormous harpoons into a target and then electrifying them.
In Godzilla vs. Mechagodzilla II, the Shock Anchors appeared initially effective against their intended target -- Godzilla. The first time Mechagodzilla used them, Godzilla was temporarily incapacitated, but he was later able to reverse the charge applied to the harpoons to counterattack, making their future value as a weapon somewhat questionable.
Diamond Coating
Opting to replace the original Mechagodzilla's shield (the "Defense Neo Barrier") with improved armor, the human engineers in Godzilla vs. Mechagodzilla II equipped the machine with an armor constructed out of NT-1 -- a metal infused with diamond coating as a countermeasure to Godzilla's beam attacks.
The same material had been used in the creation of other weapons during the Godzilla movies of the '80s and '90s, and as such had been proven as an effective defense against Godzilla. Indeed, Godzilla's atomic breath is shown to bounce ineffectually off the armored body of Mechagodzilla.
Railguns
The early 2000s saw the introduction of yet another Mechagodzilla variant, of course, accompanied by a wide range of new weapons to test against Godzilla and other enemies. Debuting in 2002's Godzilla Against Mechagodzilla, the new Mecha G (also known as Kiryu) sported a battery of high-powered railguns on the robot's arms.
The railguns don't pack quite the devastating punch that some of Mechagodzilla's other ranged weapons, like the Space Beams or Mega Buster do, but they're useful in a pinch to pepper Godzilla with lower impact strikes before closing in for a more powerful attack.
Spiral Claw
With all the different ranged attacks listed here, it wouldn't be unreasonable to assume that Mechagodzilla is optimized for long-range combat only, and would be vulnerable if its opponent were to close in. Godzilla himself has made this same mistake, only to find himself vulnerable at the hands of the "Spiral Claw" also known as the "Type-4 Anti-Beast Drilling Device."
This ability allows Mechagodzilla to rapidly rotate its hand in a drill-like fashion, lending a deadly effect to its ordinary strikes. In previous confrontations, Mechagodzilla has been able to use this weapon to brutal effect, striking huge holes in Godzilla's chest when he finds himself on the receiving end of this attack.
