One reason could be unrequited love. In the Pokemon world, Meowth has a soft spot for certain Pokemon, like the Skitty. If in a fanfiction, Skitty rejected Meowth's advances, it would make him sad. Another could be his longing for acceptance. Meowth is a part of Team Rocket, but often they don't fully appreciate his skills. He might feel sad and underappreciated in a fanfiction scenario. Also, memories of his past life on the streets, before joining Team Rocket, might haunt him and bring about sadness.
Meowth's origin story is quite interesting. He grew up in an alley where he had to fight for food. He was often bullied by other Pokémon. But one day, he saw a human using money to buy things. That's when he decided he wanted to be part of the human world. So he started learning human ways, which included learning to speak and walk like them. His journey wasn't easy, but his strong will led him to become the Meowth we know today.
However, over time, he could develop resilience. The experience of being abandoned might force him to become stronger, both physically and emotionally. He may learn to trust again, but it would be a slow process as he has to overcome the initial emotional trauma of abandonment.
Giovanni's Room isn't based on a true story. It's a product of the author's fictional writing, exploring themes and characters within a made-up narrative.
In a fanfic about Meowth evolving, it could be that a powerful enemy forces Meowth to adapt and evolve in order to protect its friends. This evolution might give it new abilities and a different appearance, perhaps more intimidating to foes.
A writer can use Meowth's body language. For example, they can describe his drooping ears, his slow and slouched walk, and his tail hanging low. This physical appearance immediately gives the readers an idea of his sadness. Also, the use of simple dialogue like 'Meowth meow (I'm so sad)' can be effective.
Sure. In the Pokémon community, there are numerous fan-created ideas. The idea of Giovanni being Ash's father has some interesting implications. It could potentially change the whole dynamic of Ash's journey. Fanfiction writers often take such unique concepts and run with them, so it's very possible to find such a fanfiction if you search in the right places, like some dedicated Pokémon fanfiction websites.
The cigar could be a key element in a heist - like plot in a fanfiction. Giovanni plans to steal a valuable Pokemon while using his cigar to create distractions. For instance, he blows smoke rings to set off alarms or misdirect guards in a Pokemon storage facility.