The relationship between Merlin and the twins could also be an interesting part of the fanfiction. Merlin might initially mistake the good twin for the evil one or vice versa. He could then find himself in a situation where he has to use his magic and wisdom to figure out which is which. And once he does, he has to decide how to deal with the evil twin without harming the good one, perhaps by trying to redeem the evil twin using his own magic and the power of friendship.
In a good twin evil twin Merlin fanfiction, the powers of the twins could be a central aspect. The good twin could have powers of healing and light, like being able to heal the wounded knights of Camelot. The evil twin, on the other hand, might have dark powers such as the ability to control shadows or spread disease. Their interactions and battles, both physical and magical, would be really exciting to write about.
One possible story could be about the good twin having to face the challenges caused by the evil twin's actions. For example, the good twin might be constantly trying to clean up the messes the evil twin makes in Camelot. Maybe the evil twin is secretly working with Morgana to bring down King Arthur, while the good twin is trying to protect the king. This creates a lot of drama and conflict within the fanfiction world.
For the good twin, you can develop their character by showing their kindness and selflessness. They could be always helping others in Camelot, like volunteering at the local orphanage or assisting the farmers. This would make them very likable.
One possible fanfiction could revolve around Merlin's twin sister Marayana having unique magical abilities that set her apart from Merlin. Maybe she has a special connection to an element, like water, and uses it to protect Camelot in her own way. She could also have a different relationship with the main characters. For example, she might be closer to Morgana in the beginning, seeing the good in her before Morgana turns dark.
One common theme is the bond between siblings. Since they are twins, their connection is often portrayed as very strong, and they rely on each other in different situations.
One great Merlin twin sister fanfiction is 'The Twin's Destiny'. It explores the relationship between Merlin and his twin sister in a world full of magic and mystery. Their adventures together are really exciting.
Marayana could be a healer in the fanfiction. She uses her magic to tend to the sick and injured in Camelot, which earns her the respect and love of the common people. This also makes her a target for those who oppose magic, as they see her as a threat to their anti - magic stance.
Maybe in the fanfiction, Uther discovers the creativity and the different perspectives on his world and characters, and he sees value in it. He might be a more open - minded version of himself in the fan - created stories.
Well, perhaps the twin sister has the power to see the future more clearly than Merlin. This ability could put her in a tricky situation as she tries to prevent certain disasters from happening without revealing too much. Or she could be a healer, and her skills are needed when a deadly plague hits Camelot. Since she's Merlin's twin, there would be a strong bond between them, and she might sacrifice herself to save Merlin at some point.
You can start by giving the evil twin a distinct appearance. Maybe they have darker hair or different colored eyes compared to the OC. Their clothing style could also be more edgy or menacing, like wearing all black with some spiky accessories.
It could change in several ways. If Merlin's twin sister is also part of Arthur's court, Arthur might be more protective of both of them, seeing them as a pair. Or, he could be more suspicious of Merlin if his sister has a different approach to magic. Maybe she's more open about it, which makes Arthur question Merlin's secrecy.
In fanfiction, Evil Merlin can be depicted as a mastermind behind many dark plots, while Morgana is the face of the chaos they create. For instance, Merlin might be the one secretly pulling the strings, using his magic to make things happen, and Morgana is the one out in the open, using her charm and power to intimidate others. They are like two sides of the same evil coin, complementing each other in their wrongdoings.