Fist Appearance: Godzilla vs. King Ghidorah (1991)
Subtitle: Strongest Monster of the Future
Origin: 23rd century cyborg created from the remains of the 2nd generation King Ghidorah.
Emergence: Created in 2204 of the VS-2 timeline, but first appeared in Tokyo in 1992 of the VS-3 & 4 timelines.
Alignment: Lawful Good (EUO)
Height: 150 meters
Wingspan: 150 meters1
Weight: 80,000 tons
Abilities: Flight, Gravity Beams, Triple Laser Beam, Triple Plasma Ray Beams, Energy Bite, Electric Cables, Machine Hand
History (VS-2): The two headed body of King Ghidorah (2nd) is retrieved from the Sea of Okhotsk in 2204 and revived by converting it into a cyborg. Mecha-King Ghidorah is still partially alive, but also has both an onboard computer in the form of M11, and can be piloted as a mecha.
History (VS-3/4): This marvel of 23rd century engineering travels back in time to 1992 to confront Godzilla in Shinjuku. Using its electified cable and the machine hand, Mecha-King Ghidorah is able to carry Godzilla out of Tokyo before collapsing into the sea after suffering heavy damage from its battle. The cybernetic middle head of the monster is recovered shortly after, and its technology is reverse engineered to create more super weapons.
Notes
1 - Similar to the note I made aboot the 2nd generation King Ghidorah, MKG's wings are very clearly completely different from KG's, they're entirely mechanical replacements and nothing of the original wings remain. It therefore makes no sense for them to be the same size, as the total wingspan is clearly smaller. Luckily, there have been a lot of different wingspans thrown aroond over the years for both KG and MKG, and of those 150m makes the most sense, as that's a difference of 12.5m on each wing, which looks aboot right if we're eyeballing it. 175 meters is the most commonly cited stat for both monsters, but, well, if Toho was trying to make all their licensed materials cohesive, they failed spectacularly, and that was kinda their one job. So, as the audience, I'm allowed to called shenanigans.
