Roses are red, violets are blue, rhyming is fun and funny, too.

In its final season, "How I Met Your Mother" is taking the gimmick episode to another level. The comedy is already known for its flashbacks (and flashforwards), musical episode, actual versions of fake websites, and a published copy of Barney's Playbook. Coming up next: an episode in rhyme!

"We just shot an episode where the entire thing is in rhyme. And it was so much fun," star Cobie Smulders told E! Online. "It's like every second line is a rhyme. It varies; you gotta watch it!"

Perhaps it will the episode when Barney and Robin marry. That would indeed be legen — wait for it — dary.

"How I Met Your Mother" is far from the first television show to pull wacky stunt episodes. Here are some memorable ones from the past:

1. "Moonlighting" - "Atomic Shakespeare": This may just be the weirdest episode in all of television history. The cast performed a variation on "Taming of the Shrew," with David and Maddie as the central couple Petruchio and Katharina. They wore Shakespearean costumes and spoke in iambic pentameter, though modern touches were also incorporated. And the whole thing was narrated by a boy whose mother made him do homework instead of watching "Moonlighting."

Watch the full "Atomic Shakespeare" episode:

2. "Hawaii Five-0": Last season, the CBS drama's producers let fans vote in real-time during an episode to determine which of three endings was used. Now, they're taking it even further and crowd-sourcing the whole episode — from the crime scene to the victim to the murder weapon to the suspects.

3. "ER" - "Ambush": Season 4 of the hit medical drama opened with a live episode performed twice (once for the East Coast, once for the West Coast). A PBS crew was filming a documentary at County General, thus the reasons for the video cameras.

See the "ER" cast after their East Coast performance:

The "ER" cast celebrates after their live West Coast show:

4. "Buffy the Vampire Slayer" - "Once More With Feeling": It wasn't the first musical episode ever, but 2001's "Once More" was a game-changer in how well-integrated it was into the story and tone of "Buffy." It was also very well-received by fans and critics.

Watch the "Something to Sing About" number from "Once More With Feeling":

5. "Mad About You," "Friends," and "Madman of the People" - The blackout storyline: Back in its "Must-See TV" days, NBC liked to do a lot of ratings stunt. This one in 1994 was a crossover without any characters actually crossing over. It started on "Mad About You," with Paul accidentally triggering a city-wide blackout. It affected the characters on "Friends" (remember Chandler was trapped in the ATM vestibule), and the ones on the short-lived "Madman of the People."

6. "The X-Files" / "Cops" crossover: The two shows seemingly had very little in common other than both airing on Fox, but they managed to meld together for 2000 episode "X-Cops." It opened like a standard "Cops" edition, with the "Bad Boys" theme and an officer being called to the scene of a crime. But once there, he found Mulder and Scully there investigating a potential werewolf sighting. (Fun fact: "X-Cops" was written by "Breaking Bad" creator Vince Gilligan.)

Watch promos for "X-Cops":

7. "Family Ties" - "A, My Name Is Alex": The normally-gentle comedy took a dark turn in 1987 with an hour-long Very Special Episode that showcased star Michael J. Fox's dramatic acting talents. In the first half hour, the Keaton family learned the tragic news that Alex's friend had died in a car crash. The second half hour featured Fox on a black stage, confronting his tortured feelings in therapy.



8. "M*A*S*H" - "Dreams": After 33 hours with little to no sleep, it's no wonder the characters of the medical dramedy had some unusual dreams. They were definitely odd — like an armless Hawkeye in a lake full of mannequin legs and arms, or Klinger operating on himself.

9. "Star Trek: Voyager" - "Bride of Chaotica": The holodeck provided the newer "Star Trek" series a lot of story fodder. In this 1999 episode, the crew is stuck in "The Adventures of Captain Proton," a callback to cheesy, black-and-white, 1930s-era science fiction movies.

Watch the trailer for "Bride of Chaotica"

10. "Felicity" - "Help for the Lovelorn": Similar to "Voyager," the sensitive WB drama took the black and white route for this gimmick episode. Creator J.J. Abrams paid homage to "The Twilight Zone" with '60s-era outfits and a spooky plot.

Watch the full episode of "Help for the Lovelorn":

"How I Met Your Mother" airs Mondays at 8 p.m. on CBS.