Mecha-King Ghidroah was originally a normal Ghidorah that survived the eradication of his species before crash landing on Terra and was sealed beneath the earth millions of years ago. He was later awoken by a monk who sacrificed his soul to awaken him in order to fight Godzilla, becoming known as Guardian King Ghidorah. Years later after being defeated by Godzilla, the Kaiju was turned into a cyborg by Cryog Commander Rhizon and the psychic twins, Minnete and Mallory.
In his original form as Guardian King Ghidorah, his appearance was almost completely identical to the original King Ghidorah, with the only difference being his heads. Guardian King Ghidorah's heads all possess a single pair of horns with a crescent located at the top of each head, while the original King Ghidorah's left and right heads' horns are more sickle-like and the central heads horns were forked and had a crescent on its forehead.
After being upgraded into a cyborg, he still resembles his purely organic form, but the horns on his heads have changed and are straighter and more devil-like, running down the sides. Not only that, but his middle-head and neck, wings, chest, knees and the tips of his tails have been replaced with mechanical parts. Mecha-King Ghidorah's cybernetic implants are all silver in color, except for the fronts of wings, which are a dark gold color, and his mechanical head possesses green eyes.
When he was Guardian King Ghidirah, he stood apart from his relatives, who destroy everything in their path, and was more of a protector. After being revived, he was determined to stop Godzilla from destroying humanity.
After his upgrade however, he was controlled telepathically by Minnete and Mallory to destroy Godzilla as well as everything else that got in his way, but when this psychic connection was interrupted, he became out of control and wildly attacked everything around him. He even retreated after being damaged by Godzilla and Anguirus.
Millions of years ago, after the original King Ghidorah wiped out the remainder of his species, Guardian King Ghidorah was the only one to successfully escape and eventually crash landed on Terra, where he remained sealed beneath the planet for millions of years.
Kingdom of Monsters Arc
In 2004, Guardian King Ghidorah is entombed within a mountain in the Himalayas in Asia. A monk goes to the temple which is build on Guardian King Ghidorah's resting place. Once inside, the monk performs a sacrificial ritual to awaken the dragon to help in stomping the other kaiju. As the monk finishes the ritual a red lighting bolt strikes one of the dragon's heads and Guardian King Ghidorah erupts from the mountain, flying towards Washington D.C where he encounters Godzilla.
The two monsters begins to battle as Guardian King Ghidorah fires his Gravity Bolts to counter Godzilla's Atomic Breath. As Godzilla is standing on Guardian King Ghidorah's body, the dragon uses all of his heads to bite Godzilla and they begin to fire the Gravity Bolts into his body. This causes an explosion which knocks Godzilla off the dragon. Godzilla soon recovers and manages to defeat Guardian King Ghidorah.
When Godila is fighting MechaGodilla, Guardian King Ghidorah reawakens and attacks Godzilla again. As Gurdian King Ghidorah and Godzilla continue to fight, MechaGodzilla fires his Anchor Cables at the two and electrocutes both of them. Both Guardian King Ghidorah and Godzilla are knocked out by MechaGodilla's Plasma Grenades.
Cryogs Revenge Arc
During the four years after Godzilla's supposed death in 2010, Guardian King Ghidorah is uncovered by the psychic twins Minette and Mallory, who then showed his injured body to the Cryog commander Rhizon (under his human alias Cryogskie). As part of their alliance, both the twins and alien seek to control the dragon. Guardian King Ghidorah has its central decapitated by Gigan and is revived with cybernetic enhancements, becoming Mecha-King Ghidorah.
In 2014, after Godzilla reappears and defeats a group of Cryog-built MechaGodzillas, Mecha-King Ghidorah is ordered to Boston. He knocks Godzilla out with his Triple Laser Beam and grabs him with his Capture Cables, carrying the kaiju king back to Siberia. In a robotics facility in Siberia, Minnete and Mallory use a machine built by Rhizon to control Mecha-King Ghidorah. As Godzilla reawakens and tries to escape the Capture Cables, Mecha-King Ghidorah attacks him his Gravity Bolts and releases Godzilla, sending him crashing into the robotic facility that has been converted into an arena. Mecha-King Ghidorah lands on Godzilla and kicks body over to two MechaGodzila drones.
As the robots hold Godzilla, the cyborg dragon fires his Gravity Bolts and Triple Laser Beam at Godzilla. Godzilla recovers and knocks one of the MechaGodzilla's in Mecha-King Ghidorah. The cyborg dragon retaliates but Godzilla slams into him and holds him down as he charges up his Atomic Breath. Godzilla knocked over the dragon with a MechaGodilla and Mecha-King Ghidorah gets back up. He bites Godzilla with his two organic heads and throws him into a building.
Godzilla fires his Atomic Breath which hits the control module that is controlling both Mecha-King Ghidorah and the MechaGodzilla units, which frees Mecha-King Ghidorah from the control of Minnete and Mallory, causing him to go berserk. Soon Anguirus joins Godzilla's side against Mecha-King Ghidorah and the remaining MechaGodzilla. Mecha-King Ghidorah has MechaGodilla slammed into him by Godzilla who tag teams with Anguirus, who knocks down the dragon. Mecha-King Ghidorah fires his Capture Cables at Godilla but accidently catches MechaGodzilla. Godzilla fires his Atomic Breath at the two, causing MechaGodzilla to explode and Mecha-King Ghidorah to become several damaged before he retreats into space. His location afterward is unknown.
Gravity Beam: From his two remaining organic heads, Mecha-King Ghidorah is capable of firing fire golden thunder bolt-like energy beams. These are similar to that of the original King Ghidorah.
Laser Triple Beam: From his central mechanical head, Mecha-King Ghidorah can fire a purple thunder-bolt-like beam of energy. This attack is often used at the same time as his Gravity Beams.
Immense Strength: Much like King Ghidorah, Mecha-King Ghidorah is strong enough to life an opponent like Godzilla over his head using his jaws to bite and left him. In the case of Mecha-King Ghidorah through, he just uses his two organic head.
Flight: Using his mechanical wings, Mecha-King Ghidorah is capable of flying at high speeds both in Earth's atmosphere and in the vacuum of space.
Capture Cables and Machine Hand: Mecha-King Ghidorah is equip with capture cables that can be launched from his mechanical body and grapple onto an opponent's limbs. From his chest, he can release an mechanical hand-like device hat can grab onto the waist of his opponent in combination with the Capture Cables. Both of these devices can also deliver a electrical shock to the opponent.