Cobie Smulders Cobie Smulders

Put away your jelly bracelets and your cool graffiti coats. It's time to break out your eyeliner and plaid shirts. Robin Sparkles is back on Monday's How I Met Your Mother — but she looks very different.

"It may be the craziest Robin Sparkles yet," executive producer Craig Thomas told reporters on a conference call. "We see a totally new part of Robin Sparkles' career in this."

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How new? Gone is the perky, denim-loving, blonde Canadian pop princess, and in her place is an angry, raven-haired grunge rocker. The dark, edgy Robin (Cobie Smulders

) will not only come as a shocker to fans, but the rest of the gang too. It all sparks from a conversation about obsession after Ted (Josh Radnor) starts dating Jeannette (guest star Abby Elliott)."[They argue about] how does one become obsessed with another person," Smulders says. "Robin sort of reveals that she was very much obsessed with somebody in her past. She acted a little bit crazy and it ... makes Barney [Neil Patrick Harris] go out there and try to find who that person is, and he becomes obsessed with finding this person. ... And at the end of the mission, he finds this video."The video is a lost episode of Underneath the Tunes (think Behind the Music) profiling Robin Sparkles, in which "we see this huge controversial moment in her career that's akin to the Milli Vanilli skipping-CD-record moment," Thomas says. The Tunes episode features cameos from a cadre of Canucks as themselves, including Jason Priestley, Rush's Geddy Lee and Paul Shaffer, with whom Thomas and co-creator/executive producer Carter Bays worked on The Late Show with David Letterman for four years. (Check out a sneak peek below.) Other Canadian guest stars include k.d. lang, NHL star Luc Robitaille, Barenaked Ladies' Steven Page, Dave Thomas, and the returns of Alan Thicke and Alex Trebek. Non-Canadian James Van Der Beek is back too as Robin's ex-beau Simon. (Yes, the robot returns as well.) "This episode takes How I Met Your Mother's Canada fetish to whole new heights," Thomas says, adding that he was shocked so many of them said yes.Photos: Stars who don't look their age There were two Canucks the show couldn't snag though: Crash Test Dummies' Brad Roberts, whom their casting director couldn't find, and Robin Sparkles' fellow Canadian teen singer/TV star Alanis Morissette. The show "tentatively" reached out to her, but "ultimately, it didn't work out," Thomas says. Nevertheless, Morissette will be deeply felt throughout the episode. The new Robin Sparkles' tune, "P.S. I Love You," is not unlike "You Oughta Know," and Robin's new look was inspired by that of the Jagged Little Pill musician. "It was a lot of fun in the hair and makeup room," Smulders says. "There were some wigs used and a lot of wardrobe changes. Any time that we get to go on set and just let things happen and just have fun — and when you're shooting a music video, especially on our show, there's no dialogue — whatever happens, happens. And we were able to create this really bizarro video."Referencing Morissette — not to mention Dave Coulier — was a no-brainer, especially when you consider the timeline of Robin Sparkles' career. "It's How I Met Your Mother's take on the '90s," Thomas says. "We've said that the '80s didn't come to Canada until '93, so now we're seeing the '90s arrive in Canada, and it proves to be very controversial."

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So will this be the final chapter of the Robin Sparkles saga? "P.S. I Love You" has been billed as the fourth and final installment, and Smulders notes that the episode "very much closes the door for her on her performing days." But with Mother officially coming back for a ninth and final season next year, anything is possible."We keep every door open, perhaps maddeningly so for many people, but we don't like to rule anything out," Thomas says. "We always want to do Robin Sparkles in a way that feels new — that we're not treading the same ground — and I think we achieved that. If we had another idea to revisit it that felt new and different from everything else, we would consider it. But we're pretty happy with this as a potential final chapter of Robin Sparkles."How I Met Your Mother airs Mondays at 8/7c on CBS.