'The McCarthys' Christmas episode to feature Alyson Hannigan LOS ANGELES, Nov. 16 (UPI) -- Alyson Hannigan has landed a guest spot on the freshman sitcom The McCarthys, starring Tyler Ritter, Jack McGee and Laurie Metcalf. The 40-year-old actress will play the Boston family's lonely upstairs tenant on the CBS show's Dec. 18 Christmas episode, EW.com reported. Hannigan is best known for her work on the hit TV shows Buffy the Vampire Slayer and How I Met Your Mother, as well as in the American Pie movies.