What happened to the humans in Equestria? Were they in another dismension or alternate universe? Was Equestria, a part of the original Earth? What happened? What if none of that stuff happened but what happened to the humans?

After 3,000 years of banishment are over and she goes to her children in excitement to see them.She now have to help twilight through her friendship lesson and go through other universe to save them from utter destruction from her arch enemy.

Celestia and Luna come upon a mysterious orb and in earth 2 girls founded a orb one they touched it they are sucked in each other's world and switched bodies and can they ever find a way back??