In our last game, the players worked their way through a series of fiendish traps into a high security vault, where they recovered a Staff of the Magi. After the game I looked at the stats, and realized that (oops!) the staff is massively overpowered for a party of level 2 players.
I don't want to just retcon akin to "You thought it was a Staff of the Magi, but it's actually X", because that seems really mean. I've already told them what it is and I don't want to just take it away by GM fiat.
So now I'm trying to think up a good in-game way to part them from the staff, which won't feel like I'm taking away their new toy. Therefore my question is:
If I have accidentally given a massively overpowered item to a party, how can I get it away from them without making them feel cheated?
Best Answer
Make it be cursed.
A very powerful item will make many adventuring parties suspicious, but if yours are just happy to go forward using it, they are in for a surprise.
I would pick an "interesting" curse that makes them wary of using it but still leaves them (technically) with the option to do so. For example, every charge used could alert some extraplanar attention, or kill a fairy or whatever you can come up with. Let them know about it somehow (ingame) after a couple of uses.
Whether this works with your party is for you to decide.