I assume the accusers would point to one or more of the following verses to back up their claims:
You shall not add to the word which I am commanding you, nor take away from it, that you may keep the commandments of the Lord your God which I command you. (Deuteronomy 4:2)
Whatever I command you, you shall be careful to do; you shall not add to nor take away from it. (Deuteronomy 12:32)
I testify to everyone who hears the words of the prophecy of this book: if anyone adds to them, God shall add to him the plagues which are written in this book; and if anyone takes away from the words of the book of this prophecy, God shall take away his part from the tree of life and from the holy city, which are written in this book. (Revelation 22:18-19)
No one should add to the commands of God or take them away. No one should add to his word at all and claim it is Scripture. No one should point to any Scripture and claim it is not God's word, thus taking away from the word of God. In obedience to the word of God, my stories commit none of these errors.
Eye of the Oracle is a fantasy story. It mentions biblical characters and stories and creates a fictional account, asking "what if" questions, thus creating a new story. My story is not true. I don't claim it to be true. In fact, I emphatically claim that the extra-biblical events that I created never happened.
Is this adding to the commands of God? Of course not. Am I claiming that my story is scriptural, and thereby adding to Scripture? Definitely not. Am I pointing to any part of Scripture and saying that it's not true? No, again. Therefore, I am neither adding to nor taking away from Scripture, and I have heeded the Bible's warnings.
Still, I am claiming that the story communicates truth in a powerful way. Since the only "what if" questions I ask are in areas in which the Bible is silent, it never contradicts Scripture, and for many readers the story shines light on what the Bible teaches in a way that is helpful and enlightening. The story communicates unconditional love, selfless sacrifice, godly perseverance, and God's faithfulness in ways that line up exactly with biblical truth.
Some people worry about my use of myths such as Lilith and Naamah or stories from the Book of Enoch. Certainly I am not the first to do this. Both Tolkien and Lewis borrowed from myths, and the book of Jude in the Bible quotes from the Book of Enoch. I think I'm in good company. I certainly can't find any Bible command that forbids the use of such things in telling a fictional story, so if someone claims that God forbids it, who, then, is the one adding to the commands of God?
Others are concerned about the presence of evil or occultic influences in my story. Yes, they are there, portrayed in all their wickedness. Evil is clearly evil, and good is clearly good. The Bible does the same, showing us what the forces of evil are like and how the children of light can overcome them. Again, I am in good company.
I tell stories to illustrate truth, fantasy stories that open our physical eyes to the unseen spiritual world. Jesus did the same. He told us of a camel passing through the eye of a needle and performed wondrous miracles. Although his miracles really happened, if they were put in a storybook that took place in another world with a name other than Jesus, it would be a great fantasy story.
I sat at the feet of my Lord and learned about using fantastic stories from the Master Himself. That is the greatest company of all.