A RKHP crossover that I think you'll like. It's just what would happen if the RK charecters were actually wicheswizards in the HP time. The summery sucks though, just read it.

YGO x HP crossover. Ryou befriends a man in the Shadow Realm and now he, Yugi and Marik are suddenly invited to Hogwarts. They wish to free his friend, but there is far more to it than meets the Sennen Eye, because Harry isn't the only one Voldemort wants