In a fanfiction where Merlin is separated from his mother for a long time and then finds out she has passed away without him being able to say goodbye. His mother is an important figure in his life, and this kind of loss would surely make him cry.
One scenario could be when Merlin loses his best friend. In some fanfictions, if Arthur is killed in a battle and Merlin is powerless to save him, he would break down in tears. He has dedicated his life to protecting Arthur and seeing his failure would be a huge blow.
Some 'Merlin Cries' fanfictions are about Merlin facing discrimination in Camelot because of his magic. The stress and sadness of being an outcast make him break down in tears. This type of fanfiction often explores themes of acceptance and friendship.
They can describe his physical reactions. For instance, 'Merlin's shoulders shook as he sobbed, his hands covering his face as hot tears streamed through his fingers.' This gives a vivid picture of his crying.
One popular one is 'The Once and Future King' fanfic series. In this, Merlin often uses the term'sire' as he plays his role as Arthur's advisor. Another is 'Camelot's Heart' where the relationship between Merlin and Arthur is very much in line with the traditional Arthurian tales, and Merlin's use of'sire' is quite prominent.
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.
There could be a fanfiction where the 'Heart of Gold' is a metaphorical concept. For example, a character, say Arthur, discovers that Merlin has a 'heart of gold' in a way that he's selflessly been protecting Arthur all along, and this realization changes their relationship dynamics. This type of fanfiction would focus more on the emotional and character - driven aspects rather than a physical object.
It could be for comedic effect to lighten the mood and add some fun to the story.
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.
One common scenario is when they are out on a quest. Arthur always puts Merlin's safety first, even if it means putting himself at risk. For instance, in a dangerous forest filled with magical creatures, Arthur would stand in front of Merlin to face any threats.
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.
One interesting scenario could be that Arthur plans an elaborate proposal in a secret, enchanted garden. He decorates it with magical lights and rare flowers. Another could be that he proposes during a grand feast, in front of all their friends and allies, making it a very public and joyous occasion. Or perhaps he takes Merlin on a quest, and at the end of it, when they've achieved something great together, he pops the question.