One possible fictional creature that fits this description could be a chimera. Chimeras in mythology are often depicted as combinations of different animals' body parts.
First, you need to study the lore of both MLP and Fairy Tail. Know the magic systems, the characters' personalities, and the settings. For example, in Fairy Tail, the magic is very diverse and each wizard has their own unique power. In MLP, the magic is more related to the ponies' special talents and the Elements of Harmony.
One popular MLP Fluttershy x Dark Creature fanfic is 'The Unlikely Bond'. It beautifully portrays Fluttershy's kindness slowly melting the cold exterior of the dark creature. Another great one could be 'Shadows and Softness' which delves deep into how their relationship develops in a world full of challenges.
There was a lizard - like creature that lived near an old, abandoned castle. This creature's tail was its most precious possession. But one day, a cruel wizard cut off its tail for a dark spell. The creature, now tailless, was filled with a new kind of rage. It started to haunt the castle at night. Its body had become distorted without its tail. It would slither through the cold hallways, and if anyone dared to enter the castle, they would feel a cold chill down their spine as the tailless creature watched them from the shadows, ready to take revenge on any human it saw.
Another common theme is the power of magic. In MLP, there are different types of pony magic, and in Fairy Tail, magic is a huge part of the story. Fanfics might have the characters combine their magical abilities or learn from each other's magic systems. For example, Fluttershy's animal - communication magic could be used in the Fairy Tail world in an interesting way. It could help the Fairy Tail members communicate with magical beasts better.
I really like 'Pony Tail Adventures'. This fanfic delves deep into how the MLP characters would interact with the Fairy Tail guild. It has a lot of humorous moments as well as some heart - warming interactions between the two sets of characters. For example, Twilight Sparkle and Lucy Heartfilia become fast friends and go on adventures together, exploring the unique aspects of each other's worlds.
Begin by creating a concept. Consider how Fluttershy and the dark creature might meet. It could be in a spooky forest where Fluttershy is gathering herbs and the dark creature is lurking. Next, develop their initial reactions. Fluttershy will probably be scared at first. Then, plan how their relationship will progress. Will it be a slow - burn friendship or something more? Outline these ideas before you start writing.
The power - up theme is also common. For example, in some fanfictions, a character from MLP might gain new powers inspired by Fairy Tail magic. This allows for some really exciting action scenes and character development as they learn to control these new powers.
Well, one unique feature is the blend of magic. In MLP, magic is often more about the natural abilities of ponies like Twilight's unicorn magic. In Fairy Tail, it's more spell - based. Fanfics combine these two types of magic in creative ways. For example, a pony might learn a Fairy Tail spell or vice versa.
Twilight Sparkle from MLP is also a common favorite. Her intelligence and magic skills can be a great contrast or complement to the Fairy Tail characters. She could help the Fairy Tail members understand the more magical aspects of the MLP world.