Willow and Oz are back together again in a "Buffy" reunion on "How I Met Your Mother."

Seth Green guest stars on Alyson Hannigan's sitcom "How I Met Your Mother" on Monday, December 17. It's a special one-hour episode starting at 8 p.m. EST that will see Barney contemplating a big decision and confiding in Ted, while Ted grapples with the information. Meanwhile, Lily and Marshall running into Daryl (Green), an old college acquaintance. Peter Gallagher also guest stars in the episode.

Take a peek at photos from "The Final Page, Part One And Two" below.

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  • "Coming Back"

  • "Coming Back"

  • "Coming Back"

  • "Coming Back"

  • "Coming Back"

  • "The Locket"

  • "The Locket"

    Pictured: Sherri Shepherd, Jason Segel

  • "The Locket"

  • "The Locket"

  • "The Locket"

  • "Coming Back"

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan, Neil Patrick Harris

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan

  • "The Final Page, Part One And Two"

    Jason Segel, Neil Patrick Harris, Alyson Hannigan

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan, Neil Patrick Harris

  • "The Final Page, Part One And Two"

    Jason Segel, Neil Patrick Harris, Alyson Hannigan, Josh Radnor

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan

  • "The Final Page, Part One And Two"

    Jason Segel, Seth Green, Alyson Hannigan

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