Perhaps he wakes up to find that the laboratory is in the middle of a big experiment gone wrong. There are strange creatures or phenomena around him, and he has to figure out how to escape and also stop whatever bad thing is about to happen. He might use his Pokémon knowledge and skills to get through this tough situation.
He would probably be very confused at first. He'd look around, trying to figure out where he is and how he got there.
In the fanfiction, when Ash wakes up in the room, he might discover that he has new, unexpected powers. The room could be a sort of testing ground for him. He'll have to learn to control these powers while also dealing with the mysteries of the room, like hidden doors and cryptic messages on the walls.
In this kind of fanfiction, Ash might wake up with new Pokemon - like abilities. For example, he could communicate with Pokemon in a more direct and profound way, like understanding their every thought and emotion just by looking at them. He might also find himself physically changed, perhaps having some physical features of a Pokemon, which could lead to all sorts of interesting adventures and interactions with his friends and other Pokemon trainers.
Well, one possibility is that Ash wakes up with all the powers of Mew. He could then use these powers to quickly become the best Pokémon trainer ever. He might be able to communicate telepathically with all Pokémon, understand their needs and desires instantly, and use his newfound psychic abilities to battle more effectively. For example, he could levitate his Pokémon during battles, giving them an unexpected advantage.
One possibility is that Naruto would initially be confused and struggle to control his new form. He might accidentally cause destruction in the village as he tries to figure out his new powers. But with the help of his friends, like Sasuke and Sakura, he could start to learn to harness the tailed beast's abilities for good, perhaps even developing new jutsu.
One possible plot could be that the OC wakes up in the world of Hayley Marshall and has to quickly adapt to the supernatural elements. Maybe they first struggle to understand their new powers, if they have any. They could end up becoming friends with Hayley and helping her in her battles against her enemies. For example, they might assist in protecting the werewolf pack from a new threat in the area.
One possible plot could be that Tyrion, now young again, uses his knowledge of the future to his advantage. He might try to change certain events that led to his hardships in his previous life. For example, he could work on improving his relationship with his family from the start, especially with his father. Maybe he'd use his wits in a different way, to gain more respect and power in Westeros without having to go through the same level of humiliation and suffering.
One possible plot could be that the OC wakes up as Natsu in a world where Fairy Tail is facing a new, extremely powerful dark guild. Since the OC has their own knowledge and personality, they might use Natsu's powers in unique ways. For example, they could combine Natsu's fire - based attacks with strategic thinking that is different from the original Natsu. This could lead to new and exciting battles and alliances within the Fairy Tail guild as they try to figure out why Natsu seems a bit 'off' but is also more effective in some ways.
He might meet Pikachu first. Since Pikachu is his closest and most loyal Pokemon friend, it would be likely that Pikachu would be by his side when he wakes up. Pikachu could be really confused at first but still show concern for Ash in his new state.
One possibility is that he wakes up and discovers new allies. The story could then revolve around him building relationships with these new characters while still holding onto his old values. He may also have to deal with the fact that the world has moved on without him and find his new place in it.