"One in the third film, I'm looking forward to meeting one of the Dementors"

Rupert Grint's quote is likely referring to the third installation of the Harry Potter movie series, Harry Potter and the Prisoner of Azkaban. In this movie, Harry Potter and his friends must face off versus the Dementors, a group of soul-sucking creatures that secure the wizard jail of Azkaban. Grint's quote suggests that he is delighted to represent one of these Dementors in the movie. This might mean that he is anticipating the challenge of playing an atrocious character, or that he aspires to explore the darker side of the Harry Potter universe. Either way, it is clear that Grint is looking forward to the opportunity to bring one of these animals to life on the big screen.