The most COMMON anti-Mormon tatic used is this verse:

Rev  22:18-19
 18 For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book:
 19 And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and [from] the things which are written in this book.

I've bolded the most forgotten part of this as well....

First - if we read this we understand that John the Beloved was NOT refering to the whole Bible - BUT the Book of Revelation instead. That's why he is specific here, "THIS book of prophecy".  Now, for some, I know that's not good enough. So we will continue.

Now, why couldn't John have meant the whole Bible? Well for one, the Bible was NOT cannonized yet. When was it canonized? There was an era of seven councils that began to cannonize the Bible. The earliest record begins in 300 AD with Eusebius of Caesarea. At this time he recorded the following, "1... First then must be put the holy quaternion of the Gospels; following them the Acts of the Apostles... the epistles of Paul... the epistle of John... the epistle of Peter... After them is to be placed, if it really seem proper, the Apocalypse of John, concerning which we shall give the different opinions at the proper time. These then belong among the accepted writings" For more on what he wrote about this go here.

Again - this was in 300 AD, when was the Book of Revelation written? Ah, well that's going to get messy as well. See, orginally some felt that the Book of Revelation was written around 95 or 96 AD - but after further research, it has been discovered that it was written aound 68 or 69 AD (for more information on this feel free to visit here p 2.

So did John forget his own words or was he committing blasphemy? Actually, neither. The scroll or book of Revelation meant ONLY the Book of Revelation. Not the whole Bible.

To go further with this, (if I still have not satisified you) IF this were true we've got problems (some I've touched on, some I haven't).

1. The first and most obvious problem is that this is NOT the first time that this type of passage has appeared in the Bible, let's look at a few others:

Deut 4:2
 2 Ye shall not add unto the word which I command you, neither shall ye diminish [ought] from it, that ye may keep the commandments of the LORD your God which I command you.

Deut 12:32
 32 What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it.

 Proverbs 30:6

      6 Add thou not unto his words, lest he reprove thee, and thou be found a liar.

So what would happen if we assumed that these verses meant the same thing as so many assume Rev 22:18-19 mean - well then, we wouldn't have the Bible....

2. IF Revelation 22:18-19 meant the whole Bible then we would have to throw out the Epistles of John as well as the Gospel of John because they ALL came AFTER he wrote Revelation...

3. IF Revelation 22:18-19 meant the whole Bible then we would have to throw out the following translations NIV (New International Version), NRSV (New Revised Standard Version), REB (Revised English Bible), NWT (New World Translation),  NAB (New American Bible) because they all ommit atleast ONE verse (although I've heard of others).

Acts 8:37

And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God.

Now some will augue that it doesn't change the message - but that is NOT the point, the point is that the Bible in these versions has had something taken out. Thus, they are accursed according to Rev. 22:19 (of course that is IF Revelation 22:18-19 means the WHOLE Bible).

4. Finally, the authority that declared the Trinity in the Nicene Creed, the authority that assembled the Books of the Bible and cannonized it and then closed the canon that ALL protestants accept - was the Catholic Church. The Catholic Church cannonized 73 Books in the Bible in both councils (Carthridge - 397, Hippo - 393). It was actually the Protestants that changed and took out 7 books from the Bible. So the entire Protestant Bible would be changed - they did this AFTER Revelation 22:18-19 was written....

It becomes clear that Revelations 22:18-19 mean ONLY the Book of Revelation and not the whole Bible which would not be cannonized for over 200 more years.

THIS MYTH HAS BEEN BUSTED!

Sources:

Biblical Canon

Adding or taking away

FAIRLDS

Biblical Studies on the web

I did want to add - that the first attempt at canon was actually by Marcion of Sinope circa 150 AD - I didn't include this because he has since been denounced as a heretic. Of him and his followers, the Catholic Church said, "they were perhaps the most dangerous foe Christianity has ever known." - Catholic Encyclepedia topic "Marcionites"