If in a Supernatural fanfiction Lucifer becomes powerless among humans, first of all, his entire view of the world would change. He has always been at the top of the power hierarchy, looking down on humans. But now, he's in their shoes. He'd likely be in a state of shock initially. Then, he might try to find a way to regain his power. But in the process, he could form unexpected alliances with humans. Some might see him as a fallen being in need of help, while others would be out to take advantage of his weakened state.
A powerless Lucifer could survive among humans by using his charm and intelligence. He's been around for a long time and has a lot of knowledge. He could use that to blend in and perhaps find some humans who are willing to protect him out of pity or curiosity.
In this type of fanfiction, a powerless Lucifer might start to experience emotions in a more raw and human way. Without his powers, he's no longer the all - powerful being. He could become a target for his former enemies who see this as an opportunity for revenge. This could lead to a series of adventures where he has to rely on his wits rather than his strength. He might also start to question his own identity and purpose, which were so closely tied to his power before.
Another plot could be that he is captured by a group of hunters who plan to keep him powerless. They try to use him as a bargaining chip with other demons or angels. But Lucifer, being clever even without his powers, tries to turn the situation around and manipulate the hunters to his advantage.
One idea could be that Lucifer has his powers stripped by a powerful spell cast by a group of witches. As a result, he's in a vulnerable state and some other characters, perhaps angels who have a bone to pick with him, decide to teach him a lesson in a rather unorthodox way like spanking. It could be a humorous take on the usually intimidating Lucifer.
In such a fanfiction, Harry's life would take a very different turn. Since Lucifer is a powerful and often mischievous or evil figure in many stories. He could introduce Harry to a world full of demons and other supernatural beings. Harry would have to struggle with his own identity and values. For example, he might be tempted to use Lucifer's power to get revenge on those who wronged him at Hogwarts, like the Dursleys or Draco Malfoy. But he also has the good nature that he got from his parents and friends at Hogwarts. It would be a constant battle between the good in him and the dark influence of Lucifer.
If Percy Jackson were to become Lucifer in fanfiction, it could lead to some really interesting storylines. He could use his new Lucifer - like status to rebel against the gods in a different way than he did as Percy. His view of the world would change drastically. For example, he might no longer see the Olympian gods as the ultimate authority. Instead, he could try to create his own order or chaos, depending on how the author interprets the Lucifer character.
It could start with Lucifer waking up in a strange place, realizing his powers are gone. Then, he's immediately confronted by a character who has long hated him. This character decides to take advantage of his powerless state and starts the spanking as a form of revenge. For example, it could be a demon who was once under Lucifer's thumb but now has the upper hand.
In a duel between God and Lucifer in fanfiction, it's a complex matter. God is all - powerful, having created the universe and all its rules. However, Lucifer is a powerful rebel. If we consider the lore, God might win as he has the ultimate power. But in some fanfictions, Lucifer could win due to his cunning and the fact that he might find a loophole in God's power. It really depends on how the author wants to portray their relationship and the rules of their fictional world.
Well, it could lead to some intense internal conflict for Lucifer. Maybe it would stir up old memories or emotions he's been trying to suppress.
Well, they might find themselves in a world full of strange creatures like vampires, werewolves, and demons. They could end up joining a group of hunters to fight against the supernatural evil. Maybe they'd discover they have some latent supernatural powers themselves.