1. The MacGuffin comes in several parts. Example: The Rod of Seven Parts
2. There are multiple organisations pursuing the MacGuffin. Goodies, baddies, neutrals, etc.
3. Activating the MacGuffin has unexpected consequences. Example: In the Corum books, once the 'ultra god' Qwll is freed he destroys both the gods of Chaos and Law.
4. Everyone knows where the MacGuffin is but only the worthy may possess it. Example: TH White's Arthurian novels.
5. The MacGuffin has no magic powers but is only required to curry favour with some NPC.
6. The MacGuffin is a place. Examples: Tanelorn, Golconda, Heaven.
7. The MacGuffin is a state of being. Examples: Tanelorn, Golconda, Heaven.
8. The purpose of the MacGuffin is to destroy someone else's MacGuffin.
9. The MacGuffin is pursuing the PCs. They want to stay away from it (rightly or wrongly).