Yes, there are. For example, some that focus on the relationship between Merlin and Arthur are quite popular. They explore different aspects of their friendship and the challenges they face in the magical world of Camelot.
Well, Morgana is quite popular in Merlin Series 6 fanfiction too. Her complex character, being both a villain and having her own reasons for her actions, makes her an interesting character to explore. Also, Gaius is often included. His wisdom and his role as Merlin's mentor are important aspects that fanfiction writers like to play with. And then there's Percival, his strength and loyalty are traits that can be developed further in fanfiction stories related to Series 6.
In 'badass Merlin fanfiction', Merlin is often more assertive. In the original series, he had to hide his magic a lot. But in fanfiction, he can be bold with his powers. For example, he might openly use magic in Camelot without fear. Also, the relationships in fanfiction can be more intense. His friendship with Arthur could be more of an equal partnership in terms of power, rather than Merlin always being in a subservient role.
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.
Well, there are fanfictions that focus on the aftermath of the events in Merlin Series 6. Some might depict how the people of Camelot adjust to a new era without Arthur. Maybe Merlin tries to use his magic more openly to guide Camelot in a positive direction. Also, there could be fanfictions where the side characters get more development. For instance, Gwaine's backstory could be explored further in relation to the events of Series 6.
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.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of 'Merlin Series Five fanfiction'. Another place could be FanFiction.net, which also has a wide range of stories related to it.
One great 'Merlin Series Five fanfiction' is 'The Lost Prophecy'. It continues the story after the events of series five, exploring Merlin's further adventures in a very engaging way. Another interesting one could be 'Merlin's New Beginnings' which focuses on how Merlin rebuilds Camelot in a different light.
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.