The truth among the lies in Merlin fanfiction can be seen in the way magic is portrayed. Magic is often a source of lies as it's hidden from most in Camelot, but the truth is that it's an integral part of the world. Fanfictions may explore the real power and potential of magic that is masked by the lies of those who fear it.
Another aspect is the political intrigue in Camelot which is full of lies. The truth might be about who is truly loyal to the throne or who is secretly plotting against Arthur. Fanfic writers often explore these themes, delving into the web of lies and trying to find the nuggets of truth that can change the fate of the kingdom.
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.
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.
Meeting his father could have made Merlin more confident. Knowing his family background and having his father's presence (even if it was just in the fanfiction) might have given him a sense of belonging. He could also become more powerful, as perhaps his father passed on some knowledge or power to him.
Arthur could be the cause. He often bosses Merlin around and doesn't fully understand Merlin's capabilities. His constant demands and lack of respect for Merlin's intelligence might push Merlin to the edge. For instance, when Arthur makes Merlin do dangerous and pointless tasks without any regard for his safety.
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.
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.