It could be because of a prophecy. If there was a prophecy that Merlin was meant to be a Dark Lord, he might start to believe in it and fulfill it. Or, he could be influenced by a dark force that has been lurking in Camelot all along, like an ancient evil that preys on his insecurities and anger, slowly turning him into a Dark Lord.
He could become a Dark Lord due to betrayal. If someone he trusted deeply, like Arthur perhaps, turned on him because of his magic, it might push him over the edge.
Perhaps Merlin discovers some dark magic that he starts to use more and more, and it gradually corrupts him. He might be initially attracted to the power it gives him, and as he delves deeper, he loses his way and becomes a Dark Lord. This could be a slow process where he starts to make small immoral choices at first, and then it escalates.
If Merlin is a Dark Lord in fanfiction, it could be an interesting exploration of the 'nature vs. nurture' concept. Maybe he turned dark because of the constant fear of being discovered and persecuted for his magic. His actions as a Dark Lord might include taking over Camelot or exacting revenge on those who wronged him in the past. It gives a whole new perspective on his character.
Well, in the original Merlin series, Merlin is mainly a hero. But in Dark Merlin fanfiction, he becomes the antagonist or at least a morally ambiguous character. His actions and motives are often much darker.
If Merlin forgets, it can create a lot of suspense. The other characters might not immediately realize what has happened, and they'll be confused by Merlin's changed behavior. This can lead to misunderstandings and tension within the group. For instance, if Merlin forgets his magical abilities, he might accidentally expose his powers in dangerous situations because he no longer has the knowledge to control them properly.
These fanfictions often explore themes of acceptance and love in a different context. They can help fans to better understand the characters on a deeper emotional level. For example, seeing how Merlin navigates his identity as a gay man in a world full of magic and political intrigue gives a fresh perspective on his character.
If Merlin has new powers or abilities in the official story that were not in the fanfiction before, it can break the fanfiction. For example, if in the original fanfiction Merlin was just a simple wizard but in the new official story he becomes an all - powerful being with god - like powers.
Merlin could be heartbroken. He might retreat into himself and become more withdrawn. After all, he has a deep bond with Arthur, and this sudden break - up would be a huge shock.
Merlin would be very worried. He would probably stay by Arthur's side day and night, using his magic secretly to try and heal him. He might also search for rare herbs or magical items that could cure Arthur.
Merlin is usually very empathetic. He'll listen to the reader's problems without judgment. In some fanfictions, he might share his own secrets and fears to make the reader feel less alone. He'll also do practical things, like bringing the reader food or making sure they have a warm place to stay if they're in a difficult situation. He'll try to show the reader that there are always options and that life is worth living.
Merlin might use his magic skills to help Harry. For example, he could use his knowledge of ancient spells to protect Harry from dark magic. Maybe he helps Harry in battles by creating magical shields or illusions to deceive the enemies.
In Merlin elf fanfiction, Merlin's character can develop in many ways. He might become more in tune with his magical side as he interacts with the elves. Since elves are often depicted as having a deep connection to magic, Merlin could learn from them to control his powers better.