Godzilla: King of the Monsters set up Mecha-King Ghidorah, but Godzilla vs. Kong killed any chance he had of joining the MonsterVerse. Before Godzilla vs. Kong, there were numerous fan theories speculating that Mecha-King Ghidorah would be Godzilla’s next villain. However, it’s hard to imagine the kaiju ever appearing in the MonsterVerse after what happened in Godzilla vs. Kong.
Introduced in the Heisei era, Mecha-King Ghidorah made only one appearance in Toho’s Godzilla franchise. His first and last fight with the King of the Monsters happened in Godzilla vs. King Ghidorah after the three-headed dragon’s death. Rebuilt with one metal head and a cyborg body, Mecha-King Ghidorah had a dramatic faceoff with Godzilla at the end of the 1991 classic. In spite of his short-lived presence in the franchise, Mecha-King Ghidorah’s popularity has endured for years, which helped make him a candidate for a MonsterVerse adaptation, especially since Ghidorah exists in its canon. But while the MonsterVerse did indeed set up his introduction, that scenario is no longer on the table.
King of the Monsters Set Up Mecha-King Ghidorah (Not Mechagodzilla)
Godzilla: King of the Monsters post-credits tease ultimately served as the basis for Godzilla vs. Kong’s Mechagodzilla twist, but it’s worth noting that the setup in the 2019 movie points more toward Mecha-Ghidorah showing up than it does Mechagodzilla. The biggest takeaway from Alan Jonah getting his hands on the head Ghidorah lost in Mexico was that the MonsterVerse was taking its first real step toward Mecha-King Ghidorah. All that was left of him was one head, but King of the Monsters made it clear that the obliteration of Ghidorah’s body didn’t matter. By establishing Ghidorah’s remarkable regenerative properties, the MonsterVerse created an easy way for Ghidorah to get most of his body back.
There’s also the matter of the newspaper headlines in King of the Monsters’ credits sequence. One of the articles, “Monarch Boosts Forces Around Skull Island,” mentioned Monarch’s efforts to make organic Titans. Their research heading in this direction reinforced theories that Mecha-King Ghidorah could be brought to life in the MonsterVerse. Monarch's work on a “mechanized giant” - noted in the same article - similarly built support for the idea that Ghidorah could get a cyborg body. This could also be taken as a Mechagodzilla tease, but Godzilla vs. Kong’s confirmation that Mechagodzilla had no Skull Island connections (and was actually built by APEX) confirms this wasn’t about him.
Mecha-King Ghidorah Can Still Be Built (But It Won’t Happen)
Perhaps in the interest of taking the less obvious route, Godzilla vs. Kong didn’t follow through on King of the Monsters’ Mecha-King Ghidorah setup and used the Ghidorah head to make Mechagodzilla instead. Theoretically, Mecha-King Ghidorah’s creation isn’t impossible, considering that the movie’s ending didn’t confirm the head’s destruction. It may have been confiscated by Monarch after Mechagodzilla’s defeat and Walter Simmons’ death. Because of that, Mecha-King Ghidorah technically could be built later on in the MonsterVerse’s future.
The problem with that, though, is that Godzilla vs. Kong reimagined Mechagodzilla as Ghidorah reborn in a robot body. So essentially, Ghidorah has now been the villain of two different MonsterVerse movies. A MonsterVerse interpretation of Mecha-King Ghidorah would increase that number to three, which is too many for one monster when Godzilla has such a massive rogues’ gallery to pull from. Not only that, but the MonsterVerse would struggle to use him in a way that doesn’t come across as a rehash of Godzilla vs. Kong’s villain story.
The MonsterVerse Made It Impossible For Mecha-King Ghidorah To Be Used Properly
Looking at how the MonsterVerse has characterized Ghidorah in its last two movies, it would be impossible for Mecha-King Ghidorah to be used properly anyway. It’s important to keep in mind that in the 1991 movie, Mecha-King Ghidorah was actually a hero. He was actually under the control of the humans, who used him to defend Japan from Godzilla’s rampages. Following along with this definition of Mecha-King Ghidorah’s character is the only way he could be unique to Mechagodzilla in the MonsterVerse, but it wouldn’t work for him to be a hero after King of the Monsters and Godzilla vs. Kong.
Ghidorah was a regular victim of mind control in Toho’s films, but that’s not a weakness shared by his MonsterVerse counterpart. That aspect of his character was on display in King of the Monsters when Jonah and Emma’s plan failed on account of the villains underestimating Ghidorah. Presumably due to his alien nature, Ghidorah went against their intentions and attempted to terraform the planet, proving that, unlike the other awakened Titans, Ghidorah can’t be controlled. Godzilla vs. Kong reinforced this notion by having Ghidorah’s spirit take over Mechagodzilla’s body. Once again, humans wrongly believed that they could use Ghidorah as a weapon. For these reasons, the MonsterVerse’s Ghidorah can only be a villain.