There are many things that could occur. Harry might find himself in a spaceship instead of Hogwarts. He'd have to figure out how to adapt his magic to the ship's technology. His friends from Hogwarts could also be there, and they'd all be exploring the unknown regions of space, using spells like the Alohomora charm to open locked compartments on alien vessels.
In a 'Harry Potter Lost in Space' fanfiction, Harry might use his magic in unexpected ways. For example, he could use the levitation charm to move around in zero - gravity. His wand might also be affected by the space environment, perhaps glowing differently or having new powers.
Well, it might be that Harry is lost at sea due to some sort of magical accident. He could meet other magical beings that are native to the sea, such as mermaids. They could either help him or pose a threat. And perhaps he has to find a way to use his Hogwarts - taught magic in new and creative ways to get back to land. He could even discover some long - lost magical artifacts at the bottom of the sea.
Well, perhaps in the 'Harry Potter finds a lost library' fanfiction, the library is magically protected. Harry could encounter some magical creatures that are guardians of the library. He might also use his Parseltongue ability to unlock a special part of the library, leading to a discovery that changes the course of his fight against the Dark Arts.
In this kind of fanfiction, Harry might feel extremely lost and depressed. He has been defined by his magic for so long, and without it, he'd have to re - evaluate his identity. Maybe he'd start to rely more on his friends, like Ron and Hermione, in different ways. For example, instead of using magic to solve problems, he'd have to use his wits and their combined non - magical skills.
It could be a dark wizard who has also found his way into space. This wizard might be using the new environment to develop even more powerful and dangerous dark magic.
Perhaps in this fanfiction, Harry loses his family's legacy. For example, something might happen to make people believe that his parents were not the heroes they were thought to be. This would not only shatter his own self - image but also make him lose the respect and support he had from the wizarding community. It would be a huge blow and make him feel like he's lost everything.
Maybe he was hit by a powerful dark magic spell specifically designed to target the soul. Such spells in the Harry Potter universe can be extremely dangerous.
Well, he might use his magic to adapt to the zero - gravity environment. Maybe he could create some sort of magical shield around himself to protect from radiation. And he could encounter strange alien creatures that he tries to understand using his knowledge of magic and the wizarding world.
He might encounter magical creatures that are native to the forest. For example, he could come across a group of centaurs. Centaurs in the 'Harry Potter' world are known for their wisdom and their own set of rules. They might either help Harry find his way out or be indifferent to his plight depending on how Harry approaches them.
In some fanfictions, Harry Potter might discover a hidden magical object in the bathroom. For example, a secret passage could be revealed behind a mirror or a sink when he's in there alone, leading him to a new adventure or a place filled with ancient magic.
Well, Harry could get involved in some really off - the - wall pranks. Since he's bored, he might decide to play some elaborate tricks on his friends, like magically changing their voices during class.