In this kind of fanfiction, it would be a really interesting twist. Ash usually starts with Pikachu, but having Gengar as a starter would change a lot of the story dynamics. Gengar is a Ghost/Poison type, which is much different from Pikachu's Electric type. This could lead to different battle strategies and interactions with other trainers. For example, Gengar's ability to phase through walls and its spooky nature could add a whole new element to Ash's journey. Maybe he would face more challenges against trainers who are used to dealing with the typical starter Pokémon types like Fire, Water, and Grass.
In some fanfictions, when Gengar gets captured by Ash, it might lead to some really interesting team dynamics. Ash could use Gengar's unique abilities in battles. For example, Gengar's ability to phase through walls could be used in creative ways during gym battles or against Team Rocket. Maybe Gengar would initially be a bit rebellious, but over time, it would grow to respect Ash as its trainer. Ash would also have to find new ways to train Gengar compared to his other Pokémon, since Gengar has different strengths and weaknesses.
In this fanfiction plot, Gengar could be the key to unlocking a hidden world of Pokémon. Since it's a Ghost - type, it might have a connection to a dimension that other Pokémon and trainers don't know about. Ash, with Gengar by his side, could explore this new world, meet new and strange Pokémon, and learn new battle techniques. Along the way, they would face challenges from other trainers who are jealous of Ash's discovery. The story could build up to a big battle where Ash and Gengar use their new - found knowledge and skills to defeat a powerful enemy and become heroes in the Pokémon world.
The story could develop in many ways. For one, Ash might enter new tournaments with Gengar by his side. Gengar's presence could attract the attention of other trainers who are either scared or intrigued. This could lead to some unique battles where Ash has to prove that he can handle Gengar well. Also, Gengar might have some secrets or a past that gets revealed as it spends more time with Ash. Maybe it was once part of an evil team but now has a chance to be good with Ash as its trainer.
One common theme is friendship. Ash and Gengar form a strong bond in many fanfictions, like in stories where they help each other through tough battles or difficult situations.
There's a possibility that it's a villainous trainer. This trainer might capture Gengar with the intention of using it for evil purposes, like using Gengar's powers to steal other Pokémon or cause chaos in Pokémon battles.
Well, perhaps Gengar is captured by a powerful trainer. The trainer might use a special Poké Ball to catch it. Then, Gengar could try to escape from the ball by using its ghostly powers.
Maybe it's a group of poachers who are after rare Pokémon. Gengar, being a relatively unique and powerful ghost - type, would be a valuable catch for them. They could plan to sell Gengar on the black market for a high price.
Well, in the fanfiction, Gengar might be held captive by some powerful villains who want to use its powers for their own evil plans. Maybe they'll try to force Gengar to haunt a particular place or to attack someone. The Pokémon trainers in the story could then start a rescue mission to save Gengar.
Well, there are several common themes. First, there's the theme of acceptance. Ash has to accept Gengar, even though it might be a bit of an odd or scary Pokémon at first. Second, the idea of transformation. Gengar could transform Ash's view of the world of Pokémon, showing him new perspectives. And third, the theme of cooperation. They often end up working together, whether it's to defeat a powerful enemy or to achieve a common goal in the Pokémon universe. This cooperation can be both in battles and in non - battle related situations, like finding a lost Pokémon or exploring an ancient ruin.