See I remembered....
So what is a macguffin? Well it depends on who you ask. But the basics is that a MacGuffin is a goal/ driving force for the plot. In Avatar the Last Airbender, the MacGuffin ( or at least for a few characters)was the Avatar. So really the plot driver can be a person, an item, or a concept...like overthowing the evil dictator. So DO NOT confuse it for a Plot Device, it's literally two different things. Also never confuse accents, even if they sound similar, people will get mad...it's a pride thing.
There are actually a lot of subtropes for the MacGuffin, and well it's hilarious, or horrible for all parties involved, when put into works. Like accidentally breaking or losing the MacGuffin.
Also consider these things when writing/creating your MacGuffin:
1)Is the nature of the item interchangeable?
and
2)Is the nature of the item irrelevant to the plot?
Now to answer the first question just think about If the object in question is of great value.This is due to the fact that there is little difference between a diamond, priceless painting or exotic statue, and the quest surrounding it would differ only trivially. To answer the second question, well, all MacGuffins have some extraordinary value, whether it be monetary, prestige, historical significance, supernatural power or forgotten knowledge. So if it answers both question, congrats, you got a MacGuffin. If it answers only one, rework somethings and you could have a MacGuffin. If it doesn't answer either questions, scrap it and try again.
Also the MacGuffin does not to be a book, and there can be more that one if it meets the criteria. However never confuse the audience as to what the MacGuffiin is.In The Lord of the Rings, the One Ring is cited to be the MacGuffin when it's not. The One Ring has this ability to corrupt anyone who comes in contact with it, and is arguably a character all on its own. However in The Hobbit, the Arkenstone is a MacGuffin: it's a priceless stone and it's relevant to 78% of the plot that ignore all the side quests.
In the Kingdom Hearts series, it is literally Kingdom Heart...It's rumored/theorized to be a sentient being of some sort. There are also a few characters that believe it's place. But there are examples of Living MacGuffins ( cases where the MacGuffin is a person), that are the Seven Lights and the Thirteen Darknesses, the first example we see were the Seven Princesses of Light and Organization XIII. The ultimate MacGuffin is the X-Blade, which would lead to another keyblade war. The series is already weird due to it being the love child of Disney and Final Fantasy.
There are the cases where of No MacGuffin, No Winner, though these are mainly stuff that pulls from mythology. One example being the Trials of Heracules, the dude had to get a couple items that belong to the gods, and stealing from all powerful deities have never ended well for most people. Plus have the time the MacGuffin have no worth, though no one finds out until the end, like the scrolls from the Journey to the West are blank...like do you know how any times Tripitaka almost died?
Like I said, just make sure you MacGuffin fits the criteria and throw in some plot twists and baddies, you'll have a great story line.