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As much as I love King Ghidorah and his constant harassment of Godzilla, I don't feel that he was a legitimate threat to Godzilla after Invasion of Astro Monster. I still consider him Godzilla's Arch-nemesis though. He practically got curb-stomped in Destroy All Monsters (I always felt a little bad for KG) and I don't feel like he was anywhere close to killing Godzilla in vs King Ghidorah or GMK. 

I personally feel like Mechagodzilla should be the top of the list, since in most of his appearances he manages to really push Godzilla to his limits, in both the original, Mechagodzilla II, and the Kiryu saga. It was a close call in all of these cases. 

I agree that Gigan definitely made a splash in his first appearance (like Ghidorah) but beyond that he didn't do much either. 

Destoroyah gets too much credit. He was somewhat challenging, and even killed Jr, but he got demolished pretty effortlessly. Of course, Godzilla was also powered up insanely by his meltdown. 

I think a character who doesn't get enough credit is Orga. Godzilla barely even scratched him during every single one of their encounters. He got bested by the ship on several occasions. Heck, he couldn't even leave a mark of Orga with his atomic breath because of Regenerator G-1. If it hadn't tried to eat him, it would have been fine.

As much as I love King Ghidorah and his constant harassment of Godzilla, I don't feel that he was a legitimate threat to Godzilla after Invasion of Astro Monster. I still consider him Godzilla's Arch-nemesis though. He practically got curb-stomped in Destroy All Monsters (I always felt a little bad for KG) and I don't feel like he was anywhere close to killing Godzilla in vs King Ghidorah or GMK. 

I personally feel like Mechagodzilla should be the top of the list, since in most of his appearances he manages to really push Godzilla to his limits, in both the original, Mechagodzilla II, and the Kiryu saga. It was a close call in all of these cases. 

I agree that Gigan definitely made a splash in his first appearance (like Ghidorah) but beyond that he didn't do much either. 

Destoroyah gets too much credit. He was somewhat challenging, and even killed Jr, but he got demolished pretty effortlessly. Of course, Godzilla was also powered up insanely by his meltdown. 

I think a character who doesn't get enough credit is Orga. Godzilla barely even scratched him during every single one of their encounters. He got bested by the ship on several occasions. Heck, he couldn't even leave a mark of Orga with his atomic breath because of Regenerator G-1. If it hadn't tried to eat him, it would have been fine.

Always good to see the MUTOs get a little love. They were some formidable opponents with that deadly tag team going for them.

I agree with much of this list, but I would have also added Kiryu 2003 to the mix. That drill looked like it was a finisher to Godzilla. Had Kiryu not gone rogue again, I'm fairly certain G man would have perished.