'How I Met Your Mother' casts Seth Green: Willow and Oz stage 'Buffy' reunion
The "How I Met Your Mother" official Twitter account announced on Friday that Green will be joining the cast in a role that will give him plenty of screen time with Hannigan.
Green will play Daryl LaCoutre, an old classmate of Lily and Marshall's. While he considered them his best friends, they barely remember him. He will appear in flashbacks, and they'll encounter him in the present-day living near campus and waiting for his much-anticipated reunion.
The episode will air in December.