Back in about 1990, a friend of mine and I decided to pull a fast one on the other players in our group. Back then, of the 7 of us, 4 were DMs. This friend of mine and I had our own campaigns and were Jonesing to do something like this.
A high-level mage in my campaign was working on a permanent portal to another world. A serious mishap occured and he ended up switching bodies with a spellcaster in the other world. He managed to figure out a way to send a message to his friends back home, but it was conveniently vague.
So the friends put their resources together and decide to plane shift to this other prime world and go looking for their lost friend. But, the same mishap occurs. They all end up switching bodies with other folks from that world.
So, in my friend's world, there are these people all running around behaving strangely. To add to the fun, none of the bodies these PCs ended up in were even in geographically similar areas. So, in addition to figuring out what the heck was going on, they had to find each other too (and it's a difficult thing to do when none of your friends looks anything like he used to).
Meanwhile, back on the prime world they left, there were these 5 strangers suddenly together, each with a new body. So, things back home, especially in regards to the PCs reputations, weren't going smoothly . . . .
It was a blast.
Dave