One sad Pokemon story could be about a trainer abandoning their Pokemon. For example, a trainer might leave their old and weak Pokemon in the wild because it couldn't keep up in battles anymore. The Pokemon would be left alone, confused and sad, having known only the company of the trainer before.
There's the story of a Magikarp that was constantly made fun of for being 'useless'. It tried so hard to be strong but was always overlooked. However, it didn't give up and eventually evolved into a powerful Gyarados, but all those years of being mocked were really sad. Magikarp was often bullied by other Pokemon in the pond, and trainers would release it quickly thinking it was worthless. But it had a hidden potential that took a long time to be recognized.
One sad shiny pokemon story could be about a shiny pokemon that was separated from its trainer during a storm. The trainer searched everywhere but couldn't find it. The shiny pokemon, alone and scared, had to fend for itself in the wild, constantly looking for its beloved trainer.
One sad story could be about a Pokemon that gets separated from its trainer. Maybe due to a storm or some unforeseen event, and it spends days trying to find its way back, feeling lost and lonely all the while.
The story of a Ditto is quite sad. Ditto can transform into other Pokemon but is often used by bad people to deceive others. It has no real identity of its own and is just a tool for mischief or worse in some cases.
Umbreon can be considered as having a sad story. It evolved due to the strong bond and feelings of loneliness and longing for its trainer. It was often left alone in the night, and this feeling of isolation led to its evolution. It shows that Umbreon has gone through a period of sadness and solitude.
Mimikyu has a rather sad story too. Mimikyu is very lonely because it is so different. It wears a ragged cloth to look like Pikachu in an attempt to make friends. However, most pokemon are scared of it when they see its true form under the cloth, which makes it even more isolated and sad.
Well, James' sad story is tied to his family. His family had high expectations for him which he couldn't meet. They were more interested in their own status and wealth. James wanted a different life, one full of adventure and freedom. In Team Rocket, he hoped to find a place where he could be himself, but things didn't go as planned. He and his partners often mess up their missions, and he has to endure Jessie's temper as well. All these make his story quite sad.
Well, it could be about a Pokemon that gets separated from its trainer. Maybe the trainer had to release it for some reason, like not being able to afford to keep it. The Pokemon then has to fend for itself in the wild, which is really sad.
Well, Cubone's sad tale begins with the loss of its mother. Cubone is often seen as a very lonely Pokemon. It wears the skull of its mother, which is a constant reminder of her absence. The skull also serves as a form of protection for Cubone. It wanders around, perhaps longing for the presence of its mother, and this sense of loss is what makes its story so sad.