My group was short one player for our D&D game this weekend, and our GM, Sam, pulled out a one-shot with an awesome twist: The three of us played wildly different — and very powerful — alternate PCs.
Our regular characters are a druid, a dread necromancer and a cleric/psion; our alt-PCs were a roper fighter, a medusa/vampire thief and a beholder. So not only was the one-shot itself a nice change of pace (as one-shots in ongoing campaigns always are), getting to cut loose with crazy characters and no consequences was a lot of fun.
The adventure was set in the fairly distant past on another plane, and while it was challenging there was little chance of the beholder — the character who had to survive to be sharing the flashback with our real PCs — biting the dust.
If you ever get a chance to work something like this in your game, take it. Sam’s approach made for a great session.