After calling on festive legend Mariah Carey to help with last year's Christmas-themed Carpool Karaoke, James Corden had big shoes to fill this year. So how did he do it? By dressing up in ugly Christmas sweaters with Reggie Watts and secretly roping in just about every star who's appeared in the segment this year to join the holiday fun. Ed Sheeran, Katy Perry, Pink, Kelly Clarkson, Sam Smith, Miley Cyrus, and more join James for a rendition of "Santa Claus is Coming to Town," but the real fun begins when James gets a very unexpected Christmas gift from Harry Styles at the end. Trust us, you're not going to want to miss this one!