The idea of Harry Potter stopping Order 66 is such a wild crossover concept, and I love how fanfiction writers twist it! One of my favorite takes involves Harry being transported to the Star Wars universe post-Battle of Hogwarts, maybe through some ancient Force artifact. He’d probably use his knowledge of dark magic to disrupt the inhibitor chips—imagine him casting a massive 'Finite Incantatem' across the clones, breaking Palpatine’s control. His experience with horcruxes might also make him sense the Sith Lord’s manipulations early, leading to a team-up with Jedi like Obi-Wan or Yoda. The emotional core would be Harry grappling with another war, this time without his friends, but finding kinship in characters like Ahsoka or Rex.
Another angle could have Harry arriving earlier, maybe during the Clone Wars, and subtly influencing events. Picture him as a shadowy figure advising the Jedi Council, dropping hints about betrayal—though they’d likely dismiss him as paranoid, echoing how the wizarding world treated him. The climax might involve Harry sacrificing himself to buy time for Jedi to escape, mirroring his canon arc. What sells these stories for me is how authors blend Harry’s stubborn heroism with Star Wars’ themes of hope versus tyranny. Bonus points if he gets a lightsaber and hilariously tries to use it like a wand first.