In RPG’s, magic can be problematical. A DM must carefully consider each and every spell and trinket given to the characters, otherwise he or she will break the campaign. The lesser magics are troublesome some times, but it is relatively easy to adjust for them. Let’s face it, DM’s can’t and won’t think of everything, every time.
Sometime you just have to let things play out and laugh at the mistake. However, I blame many bad endings on The One McGuffin getting loose.
A McGuffin is a device to further the plot. It has no other function and DM’s are well advised not create and an define an item so that it is both solution and closure to the campaign storyline.
In second edition or AD&D, artifacts were vastly overpowered magic items that really should have been left undescribed. Instead, they were tacked on the end of the magic item list, as if they were a viable option.
There is a temptation for all DM’s to use The One McGuffin as a solution to wrap up the scenario. Never, repeat, never allow characters to use an evil item for good. First, it doesn’t make sense for good to use evil for good ends. Second, as a wise man once said, “Power corrupts and absolute power is really, really neat.”
The second pen hits paper and the McGuffin is clearly defined, somewhere deep-down inside, you have decided the magic needs to be used. In all cases, this very much a Deus ex Machina story ending. If you build the characters up to the pinnacle of power, yet even from that great height, they can’t make a good ending of their own, what is the point?