A decade and a half since the cult smash Buffy The Vampire Slayer, alumni from the series are doing pretty well. Sarah Michelle Gellar last saw a lead role in the short-lived Ringer, David Boreanaz has had his own starring role in the long-running FOX drama Bones while Alyson Hannigan has followed the same suit as well with one of the lead roles in CBS' How I Met Your Mother.

Rounding out the bouts of success, Seth Green's stop motion animated and Emmy award winning series Robot Chicken has just been renewed for a seventh season while he's mostly stepped out of the network spotlight with the exception of a few guest starring roles. Now, he's stepping back in once more to reunite with one of his Buffy co-stars in an episode that promises to be legen--wait for it...dary.

THR reports that Green will guest star on the December 10th episode of How I Met Your Mother in a storyline that will heavily feature his character crossing paths with Lily and Marshall. This will be the first on-screen reunion of the duo since the series' ending back in 2003, though Hannigan has worked with Green as one of my friends who have been tapped as voices for Robot Chicken.

In the episode Marshall and Lily back at their alma mater when they run into "Daryl LaCoutre, a college classmate who looked at Lily and Marshall as his best friends -- though they barely remember who he is. They find him 12 years later, still living by the Wesleyan campus, obsessing over a reunion with the married duo."

Green and Hannigan played on-screen couple Oz and Willow for three seasons on Buffy until Green departed from the series, later reprising his role in spin-off Angel. Green has still kept many connections with the cast of the series, while this won't be the first Buffy reunion for either of them. Hannigan's husband and fellow co-star Alexis Denisof has guest starred on eight episode of How I Met Your Mother as news anchor Sandy Rivers, while the cast has contributed to Green's Robot Chicken multiple times over the course of the past six seasons.

There's still no word on whether or not HIMYM is entering it's final season, but if so it's certainly going out with a bang. Returning guest stars have included Bob Odenkirk, Ashley Williams, Michael Trucco, Becki Newton, Chris Elliott, Joe Manganiello and more. After a brief one-week hiatus due to the presidential debates, the series returns in its usual timeslot Monday at 8PM with "The Autumn of Break Ups".