Mechagodzilla is a Robot kaiju that 1st appears in Godzilla vs Mechagodzilla. When Mechagodzilla is 1st encountered , he's wearing a costume called Fake Godzilla. During this time Anguirus rips a hole in Fake Godzilla's flesh. After a while Godzilla arrives and fights Fake Godzilla then after a bit Fake Godzilla becomes Mechagodzilla. Later on King Ceasar gets summoned and Godzilla helps him defeat Mechagodzilla. Then long after Mechagodzilla get's rebuilt and this time he's allied with a dinosaur called Titanosaurus. Godzilla this time kills Mechagodzilla by battling him til Casura passes on. The parts of Mecha-King Ghidorah that are part robot get salvaged to create Mechagodzilla 2. One of the encounters Mechagodzilla 2 had was fighting with Fire Rodan. When Godzilla arrived , Mechagodzilla 2 becomes Super Mechagodzilla. Super Mechagodzilla overpowers Godzilla's 2nd brain. Fire Rodan sacrifices himself to save Godzilla. Then Super Mechagodzilla was destroyed.
Both Super Mechagodzilla and the Showa Mechagodzilla are featured in the PS4 Godzilla game. Mechagodzilla has a lot of weapons. The YouTube channel Scifi Explained showed that Mechagodzilla had a few weapons that were unused.