One popular one could be 'The Hilarious Adventures in Fairy Tail Guild'. It has a series of short stories within the fanfiction that focus on the comical interactions between the guild members. Another is 'Fairy Tail's Funniest Pranks' which is all about the various pranks the characters play on each other.
You can try some popular fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of 'Fairy Tail' fanfictions, including those about funny moments.
One of the funniest scenarios could be when Happy tries to 'help' Natsu cook but just ends up making a huge mess. He might accidentally add too much of an ingredient or knock over pots while flying around the kitchen in excitement.
Cana could be embarrassed when she tries to show off a new card - based magic technique to the younger members of Fairy Tail. But she messes up the incantation and instead of a cool display, she creates a bunch of sparkly but useless card confetti that rains down on her, making her look silly.
One idea could be that Happy's death shatters the Fairy Tail guild. Natsu, being his closest friend, goes into a deep depression. The guild loses its usual cheer and the members struggle to come to terms with the loss. They might hold a grand memorial for Happy, and throughout the fanfiction, it could show how each character copes in their own way, like Lucy writing in her diary about all the memories she had with Happy.
There's a fanfiction called 'Happy and the Lost Treasure'. In this story, Happy teams up with some unlikely allies in search of a legendary treasure. It has a lot of humor as Happy's antics keep the other characters on their toes. The story also has some really cool action scenes where Happy uses his flying skills to outmaneuver enemies.
In the case of Pearl and Sky, when Sky made a special floating platform for Pearl so she could experience flying for a little while. It was a moment that symbolized their willingness to share their different worlds with each other, and it was a beautiful display of their love.
One idea could be that in their human forms, Happy and Carla are part of a detective agency in Magnolia. Happy is the enthusiastic junior detective while Carla is the more serious and observant one. They solve mysteries related to magic items that have gone missing, often running into other Fairy Tail members who unknowingly hold clues.
In this kind of fanfic, the key elements often involve Happy's new abilities as a dragon. For example, he might have the power to fly faster and breathe different types of magic breaths. Also, the story could explore how Happy copes with this new identity. Does he feel isolated at times? How does he interact with the dragon community if there is one in the fanfic? These are all important aspects.
Another possibility is an accident within the story. Perhaps during a chaotic battle or a magical experiment gone wrong, Happy could be caught in the crossfire or affected by some unforeseen magical consequence. This would be a tragic turn of events for the usually cheerful and helpful Exceed.