One interesting adventure could be Merlin using his magic in a creative way to save Camelot from a mysterious plague. Maybe he creates a magical barrier around the city to keep the illness out.
One great fanfiction in this area could be about Merlin's training in a secret magical realm. He might learn new spells and techniques from ancient magical beings that no one in Camelot has ever heard of.
They could have adventures where they explore ancient magical places. Maybe they find a long - lost magical artifact that has the power to change the fate of Camelot. Merlin, with his knowledge, and Aithusa, with its dragon abilities, would be a formidable team in such quests.
Morgana might also be involved. If she were to travel through time, she could either try to change the past to gain more power in the present or she could be sent to the future to see the consequences of her actions. This might lead to a change of heart for her, or it could make her more determined to achieve her goals depending on what she witnesses.
Magic and mystery are likely main themes. Merlin is a well - known figure associated with magic, so the novel probably explores his magical powers and the mysterious world he inhabits.
They could have an adventure where they help Camelot defend against a dark sorcerer. Harry's combat magic from Hogwarts would be useful, and Merlin's knowledge of Camelot's magic and its secrets would be crucial. Another adventure might be to find a lost magical artifact that is important for both Camelot and the wizarding world. Along the way, they might encounter magical creatures unique to Camelot that Harry has never seen before, like the Questing Beast.
They could go on quests to find ancient family artifacts. Maybe there's a magical sword or a powerful amulet that has been in their family for generations. They would set out to retrieve it to protect their family's honor or to use it to save their kingdom.
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.