Regardless of the additional season granted to 'How I Met Your Mother' fans, this coming Monday's all-new episode "P.S. I Love You" will prove an important part of the show's mythology, as Robin comes to grips with both her past as Robin Sparkles, and a new stage of her relationship with Barney. And what better way to show that, than with an all-new musical number? Preview the downfall and gothic turn of Robin Sparkles inside, with an all-new 'How I Met Your Mother' clip!

Not only will Monday's all-new 'How I Met Your Mother' episode "P.S. I Love You" bring with it a number of of Canadian guest stars, but also what could be the final chapter in the "Robin Sparkles" saga from Robin Scherbatsky (Cobie Smulders)' Northern past. Both Smulders and co-showrunner Craig Thomas previewed the episode to reporters, outlining the startling change in Robin Sparkles' appearance, caused by an obsession with an unknown figure.

Thomas also teased that the new track from Robin Sparkles borrows a hint of Alanis Morissette, whom producers initially sought to join the many Canadian guest stars, but to no avail.

When we were recording the song in the music studio, we were pushing Cobie to go for it and go completely insane. There were a few takes where she had so much fun going really big and full-throated screaming and insane, and and I think she thought maybe we weren’t going to use those takes. Well, we did. Sorry, Cobie. It’s fantastic and bizarre.

‘Growing Pains’ star Alan Thicke, ‘Late Show’ bandleader Paul Shaffer, ’90210′ hunk Jason Priestley, ‘Jeopardy’s Alex Trebek, K.D. Lang, Barenaked Ladies frontman Steven Page, Rush frontman Getty Lee and Canadian former hockey star Luc Robitaille will all appear as themselves, while ‘Dawson’s Creek’s James Van Der Beek’ will reprise his role as Robin’s old boyfriend Simon. Canadian actor Dave Thomas will portray music agent Chuck Gerusi, while ‘SNL‘ vet and Chris Elliot’s daughter Abby Elliot will appear as Ted’s jealous new girlfriend Jeanette, reinforcing the theme of "obsession."

"P.S. I Love You" may not prove the last we see of Robin Sparkles, given the ninth season order, but Thomas admitted to being happy with the episode as a potential final chapter. Check out another clip of 'How I Met Your Mother' episode "P.S. I Love You" below, and tune in on Monday to see for yourself!