Good supernatural power exists. So does evil supernatural power. Each has similar qualities, but their employment and outcomes are completely opposite.
Yet telling them apart in fiction can be challenging. Yes, many Christian fantasies don’t mention magic, and they associate witch with evil and prophet with good, just like in the Bible. A good example of this is C.S. Lewis’s White Witch: in The Lion, the Witch, and the Wardrobe she is described as “a perfectly terrible person” and “bad all through.” That conforms to the biblical idea of witches, i.e. they are evil.
However, you will eventually run into the problem of semantics; words can take you only so far in a language that’s always changing. Secular fantasy has twisted words like seer and prophet. Christians struggle to find ways to describe supernatural power, often falling back on back on the collective lingo of fantasy. Therefore we must dig deeper.
First, in the Bible we find many non-human beings wielding abilities far beyond human capacity with no condemnation (e.g. angels). Likewise, fantasy births many non-humans able to perform supernatural acts. Now if it isn’t wrong for angels to wield supernatural power, why would it be for fairies and elves and other such characters?
Again consider the White Witch: C. S. Lewis writes, “She’s no daughter of Eve…there isn’t a drop of real human blood in the Witch.” She isn’t human. Nor is Aslan. The humans in the story—Lucy, Edmund, Susan, and Peter—have no “magical” power. You see the same in The Lord of the Rings. The ones who have supernatural powers—elves and wizards—aren’t human, while the humans Aragorn and Boromir have no special abilities beyond normal giftedness (e.g. Aragorn’s healing ability, which isn’t instant nor guaranteed like supernatural healing).
But what about humans with supernatural abilities? They also exist in real and fantastical worlds. And like in the real world, we must be discerning, comparing the characteristics and uses of those supernatural abilities to the biblical equivalent. Is the power of the good characters greater than that of evil? Do their powers heal or destroy, bring life or death? To whom or what do they credit their power? Can the character summon the magic on whim?
In short, perhaps John White’s character Mab the Seer sums it up best in The Sword Bearer:
“Sorcerers, wizards, magicians—they chose to serve themselves. They want their own power. They want magic…It is true I have power…but it is [God’s] power…It is to be used in his service. Magic is stolen power.”