Earth
The planet we're on. Was destroyed in at least two timelines. Turned into an apocalyptic wasteland in the third.
Big Bad Timeline
In Member OG, the Western Hemisphere was destroyed by Lupus's laser that was supposed to destroy the entire world after SwordMaster accidentally activated it (when only half the world was destroyed, Lupus mused his regret at having traded its Contractor Core for an EXP Egg). But it got better, actually I think it was only restored in the non-canon Member OG 5s as well as the last Christmas Member OG post which I don't count anyways as a way of making the status quo easier to understand for newcomers. But then in Member OG 5: Secret of the Ooze, Akujin used an X-Bomb to blow up Earth so that he could search the rubble for the four stones that sealed away the Writer's Chair. He was unable to complete this task, as the OG Six kept him busy on Krad, and Earth (Western Hemisphere included) was restored when BSD made a wish to the Holy Plot Device (reverb). Most were unaware that the planet had even been destroyed.
Control of the planet was largely split between Team Rocket Omega in the Western Hemisphere and TWIFATIT in the Eastern Hemisphere. In Member OG 8: This Title is irrelevant, the Earth was squished flat when Lupus used the Limitless Drive to collapse the three dimensions. It was restored in Member OG 10: Full Circle. Following Lupus's death and the subsequent collapse of his organization, the governments of Japan, Canada, Italy, Portugal, Venezuela, and the New Oceanic Republic joined forces as the United Super State Region (USSR). They formed a peacekeeping team with the help of refugee Kradians to retake the planet from TRO and other evil forces, but were probably collapsed when Lupus was resurrected and brought TWIFATIT back with him.
In The OGers: The Third Generation, TRO collapses when the OGers destroy their main headquarters and Magikoopa gives up his position. In the wake of their fall, TWIFATIT begins to claim their territory.
Good Ol' Timeline
The world remained hunky dory, though in Gamehiker Member OG 2 it was nearly taken over by an Ushutarian invasion. In the year 2065, the Earth was seemingly destroyed when the Ushutarians returned, but it was instead swapped with a decoy (Anti-Space Earth) while the real Earth was hidden inside of Anti-Space. The survivors established colonies in the Sol System while making Mars the base for human population.
Other Lands
The setting of the Pikmin OG. According to Greg: "Plot twist. It was Earth all along!"
Quotes
~Sapphire's spirit reaches the other side of the planet.~
Sapphire: ...So we need to set off a tremendously large explosion in the next five minutes and six minutes. The farther from the center of the Earth, the better.
Luigiman: ~shuffles around in the pockets of his shorts~ Well, I have some stuff from Fuzzball, but they won't create huge explosions... unless we use the volcanoes! The chain of island volcanoes we're sailing amongst will work perfectly! Just toss a few inciniary devices down and we're set!
Kuria: Won't we cause a lava flow that way?
Vorpal: That's what running is for.
~Soon, on the flip side of the Earth, Fusion, SwordMaster, and Kantii are beaten up at Eerie's hands, while Legion keeps an eye on his army. Just when all hope is lost, Eerie flies up into the air for a bit before turning around and smacking into the Earth upside-down. When GORE's party had set off an explosion, it rocked the Earth, causing it to flip over. Everything remained the same, though, relying on the Earth to provide gravity. Eerie is not bound by gravity, however, and thus got the Earth thrown at him.~
-Even the flat Earth can be used as a weapon in Member OG 8: This Title is irrelevant