This comes, as somewhat a reunion with major star of the show, Alyson Hannigan in which he co-starred with in hit TV series Buffy The Vampire Slayer.
Seth will play a "creepy" guy named Daryl who thinks Lily (Hannigan) and Marshall (Jason Segel) were his BFFs in college. The only hitch? They barely remember the guy, and now he is obsessed with having them both in his life.
Green is scheduled to make his first appearance on December 10th.
Source : TVGuide.com
Are you excited to see Alyson and Seth on-screen together once more?