Game of Thrones has really mined the cast of Harry Potter for its characters, with the likes of David Bradley (Argus Filch and Walder Frey), Michelle Fairley (Mrs Granger and Catelyn Stark) and Ciarin Hinds (Aberforth Dumbledore and Mance Rayder) all appearing in both series. There have been nine in total, some of whom were just minor characters in both, but the show has most obviously referenced this with Osha, the wildling played by Natalie Tena. She played Tonks in the Potter films, and when we meet her in season 1 shes making a broom, with a few other shots showing them as well. Just dont call her Nymphadora.