The group needs to collect and destroy not one, not ten, but hundreds of MacGuffins in order to succede in their task. The catch is that the MacGuffins are actually ANY magic item, even those of no significant rarity or power, and a certain ammount of stored power (the XP needed to create the item) needs to be freed from them in order for something kewl to happen. There is no single specific object that needs to be found and the PC's can go about colecting the MacGuffins in any way they choose.
That's basically the plot of Book 3 in the Alsatia game. There is a finite ammount of magic energy in the plane, and the Book 2 BBEG made WAY too many magic items with the help of Hell. Now, magic is declining rapidly and we need to replenish the plane's stores. Unfortunately, many of the magic items were brought to another plane, and our plane has been magically 'locked' to prevent any planar traval (and draining more magic power because fo the lock.)
- Kemrain the MacGuffin.
Tell me you didn't see that one coming.
- Kemrain the Unorigional.