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.
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.
In a more humorous take on the 'Merlin tied to a bed' fanfiction, it could be that Merlin has fallen ill and the overly - protective Gaius has tied him to the bed to make sure he rests. Merlin, being the active person he is, complains constantly. Arthur comes to visit and teases Merlin about finally being still for once. Meanwhile, Merlin tries to convince Arthur to let him loose, promising that he'll be fine. Eventually, Gaius relents and unties Merlin, who then immediately starts bustling around the room.
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 died in the fanfiction, it could trigger a series of tragic events. The balance of power could tip, and the villains might seize the opportunity to attack. It could also bring out hidden strengths in the remaining characters as they try to cope with the loss.
One great 'Dark Merlin Morgana' fanfiction is 'The Dark Alliance' which delves into their complex relationship as they form a powerful and somewhat menacing pact in a world filled with magic and political intrigue. It's really interesting to see how their characters evolve in this darker setting.
One more idea is that Merlin is tied to the bed in a dream - like state created by an ancient magic. In this dream world, he is faced with his deepest fears and insecurities. His friends in the real world notice his strange behavior and try to wake him up. Merlin, while in the dream, has to find the source of the magic that is binding him and break free. Through his inner strength and the memories of his friends, he manages to do so and wakes up, having learned more about himself and his magic.
The theme of a dark destiny also runs through many 'Dark Merlin Morgana' fanfictions. It's about how their actions, when they embrace the dark side, lead them on a path that is different from the traditional heroic or 'good' destinies. It often involves them trying to reshape the world according to their dark ideals, which can be both fascinating and terrifying to read about.
There is also 'Merlin's Shadowed Destiny'. In this story, Merlin is influenced by a dark prophecy and begins to make choices that lead him away from his traditional role as Arthur's protector. It shows how his character can be manipulated by the allure of dark magic.