In my fantasy novel, the main Antagonist is a King, who is also host to a spirit. This spirit wishes only for one thing: to find a specific amulet, which is required for him to achieve his full power. The King, who is merely a host, has an internal struggle against this spirit, which is unfortunately too strong. This just seems too one sided, too black and white. I don't want the spirit to be "just evil", but then again I don't see how I can make him not.
Let us ignore the "what is evil" argument for now. What will "full power" let said spirit do. What exactly does it DESIRE out of its existence that it does not already possess. Was the spirit pulled into the world from elsewhere to serve some "petty wizard's" goal and just wants to go home? Spirit, demon, man, or cat...What does it WANT? Power is a tool. It helps pave the road to your destination. Where exactly does the spirit want to go?
I agree with the above post. The character's motivation is what needs to be made clear. Even if the spirit is just pure evil, like Sauron, if we know what he wants, then he will be remotely understandable. Not every villain needs to be relatable or completely understood, but they need to have a desire that drives them. Sauron, wants total control. That's it. He is evil; he wants absolute control and death of his subordinates. Contrarily, Lord Voldemort seems like a black and white evil, but he really had to deal with having power while living as a nobody. He had issues with inferiority that carried into his obsession with power and purity. Darth Vader seemed like the embodiment of evil (the Dark Side), but he really wanted order and power. The real evil was the Emperor, who only wanted absolute power; there was nothing relatable about him. My point is, your characters don't need to be entirely reliable or understandable, but they need to be developed with their on goals and desires. Those desires are what make characters realistic and interesting. As CrimsonReaper said, why does the spirit want power? What can it attain by gaining power? Maybe it wants power so it can reclaim lost control over the realm. Or maybe it has to prove itself in the spirit world. Or maybe it is just prideful and wants power to subjugate the realm because it can. Or maybe it wants to destroy everything and rebuild. Why does your spirit want power? Where does the spirit come from? Why is it here? Are there any restrictions to his mobility? These reasons might help you develop him more.
Is he going to replace mankind with anything or is he just going to sit around alone once we're gone? I ask because if he is doing it to benefit some group it gives him a less completely "I'm evil for the sake of it" vibe, even if his choice of replacements are demons or something.
Perhaps the dragons need to move to this new world because of something bad happening to them in their own, or they need something that they can only get here, to makes their eggs hatch maybe? Anything really. But it gives the King (spirit) a motive other than simple mustache curling evil.
Alright, so why does he want his full power so bad? Is it the only way he can revive his dead lover? Is there some kind of unseen threat that he needs to achieve full power to stop? Something else? It's your choice, but just ask yourself "how can I make the spirit an anti-villain?" Or "Anti-villain," depending on which suits your idea of how you want the spirit to be.
