There are also fanfictions where Ash catches Rayquaza. This could be set during a time when the sky is in chaos due to some dark energy. Rayquaza is drawn to Ash because of his pure heart and determination. Ash, with his usual courage, teams up with his pokemon to assist Rayquaza in restoring balance. As a result, Rayquaza allows Ash to catch it.
Maybe a story about a human who accidentally stumbles into the hidden realm of Legendary Pokemon. There, they form a friendship with a Legendary that is an outcast among its kind. Together, they try to change the perception of the outcast Legendary in its own community while also finding a way for the human to return home.
Team Rocket would be the most obvious ones. They're always after rare and powerful Pokémon or Pokémon - related items, so the legendary egg would be a huge target for them.
Often, Ash has to complete a quest. In a fanfic with Ho - Oh, Ash might have to find three special feathers scattered across the region. These feathers are said to be the key to summoning Ho - Oh. As he embarks on this journey, he faces many challenges and overcomes them with his existing Pokemon team. Once he collects all the feathers, Ho - Oh appears and, impressed by Ash's determination, decides to fight alongside him. Another way is through a prophetic vision. Ash might have a dream that tells him how to find and bond with a Legendary like Entei, and he follows this vision to make it happen.
There's also 'Legendary Pokemon: The Forbidden TF'. This fanfiction delves into a darker side of pokemon transformation. It involves an ancient spell that forces legendary pokemon to change forms, leading to a series of events that endanger the pokemon world. It's really exciting to read as it unfolds the mystery behind the transformation.
A strange and rare item could be the cause. Maybe a Vulpix stumbles upon an ancient amulet that has the power to transform Pokemon. Once the Vulpix touches it, the transformation occurs. This amulet could have been lost for centuries and have some sort of legend associated with it.
It could be Mew. Mew is known for its ability to transform and has a very mysterious nature. If Ash was Mew's son, he might inherit some of that mystery and the power to communicate with Pokemon in unique ways.
When Celebi initiates the transformation, it's like a wave of emerald light washes over the target. First, there's a tingling sensation all over the body. Then, the physical features begin to shift. If it's a transformation into a flying - type Pokemon, the back might start to bulge as wings start to form, feathers sprouting out in a flurry. The face would change too, the nose becoming a beak perhaps, and the eyes taking on a different shape and color. Every detail of the transformation can be described in a very tactile way, making the reader feel as if they are witnessing it firsthand. You can also add in the sounds, like a soft whooshing as the transformation energy moves around.
In many fanfictions, Ash's shadow Pokémon transformation can be a really cool concept. It might happen due to some dark energy or a special encounter. For example, he could be influenced by a shadowy force while exploring an abandoned Pokémon facility. This transformation could give his Pokémon enhanced, but more aggressive powers.
He could gain the ability to use Pokemon - specific techniques in combat. For instance, he might be able to use Quick Attack, which would make him move at an incredibly fast speed, much like his own speed - based jutsu in Naruto. His opponents would be caught off - guard by these new moves.