Where is “Scripture only” found? In Scripture of course, not some extra-Scriptural doctrine, as the author claims, which would be self-contradictory.
Mark 7:8
For laying aside the commandment of God, ye hold the tradition of men, as the washing of pots and cups: and many other such like things ye do.
Colossians 2:8
Beware lest any man spoil you through philosophy and vain deceit, after the tradition of men, after the rudiments of the world, and not after Christ.
Revelation 22
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.
Examples abound of those who went beyond Scripture and paid the price, Moses, Saul etc.
But what of the Traditions of God? When the Apostles were sent forth, they didn't have Bibles with them. The only Scripture they brought was the Old Testament. The New Testament was the word of their testimony... the Tradition born out of the Lamb of God Himself.
Revelation 22
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.
How many books are there in the Bible? It's an important question to answer your challenge because Revelation is but one in a library of books. And, by the way, there is no way Revelation could stand on its own. It is a summary of the history of salvation completely impenetrable without the rest of Scripture and Tradition.
Dear friends, although I was very eager to write to you about the salvation we share, I felt compelled to write and urge you to contend for the faith that was once for all entrusted to Gods holy people
Jude
But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let them be under Gods curse!
Gal 1:8
I am NOT by any means a perfect nor near perfect Christian but my ability to read is fairly certain.