There are fanfictions where Merlin's omega nature makes him form a special bond with the magical creatures in Camelot. This bond then helps him save the kingdom in unexpected ways. For example, he could communicate with a dragon who gives him crucial information.
You can try Archive of Our Own (AO3). It has a large collection of fanfictions, and you can easily search for omega merlin fanfiction using the search bar. Just type in the relevant tags.
Well, 'Destined Mates: Arthur and Merlin' is also a wonderful piece. It delves deep into how their alpha - omega connection affects not only their relationship but also the fate of Camelot. It's full of adventure and the development of their bond is really well - written.
Another theme is the forbidden love aspect. Given their different roles in society, their relationship might be seen as unacceptable in the context of the story's world. This adds a layer of drama and tension. Some stories also focus on how they overcome these societal barriers. Moreover, magic is usually a big part of it, as Merlin is a powerful magic user. His magic can either be a source of conflict or a way to bring them closer together.
Fanfiction.net is another place. There are numerous stories on this site as well. However, the tagging system might be a bit different, so you may need to do a bit more digging. But it's definitely worth checking out for this type of fanfiction.
You can try fanfiction platforms like Archive of Our Own (AO3). It has a vast collection of fanfictions in various categories, including Omega Merlin x Alpha Arthur ones. Just use the search function and type in relevant keywords.
Arya Stark is sometimes reimagined as an omega in fanfiction. Her skills as a faceless assassin could take on a new dimension in an omega - centric story, using her stealth and ability to change identities to navigate the challenges of being an omega in a harsh world.
One great female Merlin fanfic could be one where she uses her magic in unique ways to save Camelot. For example, in a story she might use her powers to heal the knights secretly when they are injured in battle. This would add an interesting twist as she has to hide her actions from Uther.
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.