10 best TV crossover episodes

The best of both worlds

The TV crossover is a curious event. A melding of two separate universes previously thought to exist on their own, it throws up all sorts of questions and queries, spawning a whole line of debate on what it all means. Of course, if arguing about canon and continuity isn't your bag then those episodes can be enjoyed for the brief flashes of fun that they offer long-time TV audiences.

Unlike their cinematic counterparts, TV crossovers often take more liberties. See, if the two concepts thrown together for a one-off story don't quite gel - the next week things simply return to normal. Ergo, they're a bit riskier and can often be a source of much glee for fans. Here we rundown some of the best to ever hit the box.

Mork & Mindy - Happy Days

The episode: Mork and Mindy, "Pilot"

The crossover: Even though the fact hasn't been kept quiet, it's not commonly remembered that Mork & Mindy is in fact a Happy Days spinoff. And so, the show's pilot episode introduces the world to the two hapless aliens as Mork (Robin Williams) is transported to our planet and bumps into The Fonz. Brilliant performances marks this as a hugely influential pop. culture happening.

Best moment: When Laverne & Shirley is roped into things - also a Happy Days spinoff, as Mork goes on a blind date with Laverne.

Friends - Mad About You

The episode: Friends, "The One With Two Parts"

The crossover: When Lisa Kudrow landed the role of Phoebe Buffay on Friends after she'd already appeared on another NBC sitcom , the network cooked up a way to avoid confusing easily perplexed viewers. She would play twin sisters. So when Mad About You's Helen Hunt and Leila Kenzle appear in Central Perk they mistake Pheebs for Ursula. It sounds like a cheap shot, but the concept proved effective thanks to Kudrow's performance across both shows.

Best moment: When Phoebe's suitably wacky response does nothing whatsoever to help the mistaken pair.

Arrested Development - Law & Order

The episode: Arrested Development, "S.O.B.S."

The crossover: Richard Belzer first played the character of Detective Munch on Homicide: Life On The Streets and reprised the role across a host of popular TV series. One of which, quite possibly the most unlikely candidate, was Arrested Development that plants Munch in Tobias' scrapbooking class in an attempt to get the nitty gritty on the Bluths.

Best moment: The examples he uses to entice Tobias are all amusing, with the above picture perhaps the wittiest.

Community - Cougar Town

The episode: Cougar Town, "Something Good Coming"

The crossover: Throughout Community, geek extraordinaire Abed (Danny Pudi) constantly lavishes praise on Cougar Town claiming it's one of his favourite shows. So during season two when he tells Jeff that he's been given an invitation to visit the set, he winds up filming a cameo. That turns up in an actual episode of Cougar Town. While Laurie is lecturing Travis outside Subway, Abed is clearly visible in the background.

Best moment: Abed tries so damn hard to look as though he's casually supping a coffee then ends up staring at Laurie before running away.

The Simpsons - X-Files

The episode: The Simpsons, "The Springfield Files",

The crossover: At the height of The X-Files popularity its leading stars were given a rare opportunity; instead of playing themselves in cameo form David Duchovny and Gillian Anderson remained in character for a special episode of The Simpsons. The pair head to Springfield to investigate Homer's claims that he'd been visited by extraterrestrials.

Best moment: The reveal of Mulder's ID badge. The picture is him in a swimsuit.

Buffy The Vampire Slayer - Angel

The episode: Angel, "I Will Remember You"

The crossover: Alright, so Angel is technically a Buffy spinoff but this still counts. A self-contained episode throwing those two star-crossed lovers back into each other's arms, it's a wonderful pause for vamp and slayer as he's restored to human form and the pair share a night together. It's all terribly romantic and therefore all the more devastating when Angel time-hops (turns out he's rubbish at fighting as a human) back to become a soulful vamp again.

Best moment: And by best, we mean "bit that will make you sob" : when Buffy practically begs Angel to not undo their time together.

The Simpsons - Family Guy

The episode: Family Guy, "The Simpsons Guy"

The crossover: For an hour-long special event one of the longest-running animated series joined forces with one of its newest contemporaries. The result? A madcap mash-up instigated when the Griffins' car is stolen on the outskirts of Springfield. Peter befriends Homer who then invites the Quahogians to stay with the Simpsons, and the two families duke it out.

Best moment: A riff on Family Guy's chicken fights has Peter and Homer engaged in an epic scrap that borders on the ridiculous.

Batman - The Green Hornet

The episode: Batman, "A Piece Of The Action"

The crossover: After brief background appearances in an earlier episode, The Green Hornet and Kato come to the aid of Batman and Robin helping the costumed pair investigate a counterfeit operation in Gotham. The ads promoting the episode described it as a "dynamic duel of dynamic duos" that's probably the best summary of one of the first superhero crossovers.

Best moment: When The Green Hornet and his sidekick deliberate on how they should best approach Batman and Robin. It's heavy on the exposition which makes it all the more charming.

The X-Files - Cops

The episode: The X-Files, "X-Cops"

The crossover: Before he went on to create Breaking Bad, Vince Gilligan was credited with penning some terrific X-Files episodes including this one. Mashing up Mulder and Scully's antics with the lo-fi Cops series - one of Gilligan's favourite shows - spawned one of the most popular X-episodes in which the two Special Agents are interviewed by police during one of their investigations. The shaky, found-footage camera style adds a layer of extra heebie-jeebie to the monster.

Best moment: On the whole, Scully getting irritated by being followed by the cameras. Brilliant.

Doctor Who - Torchwood - The Sarah Jane Adventures

The episode: Doctor Who, "The Stolen Earth" / "Journey's End"

The crossover: To mark the close of Russell T. Davies' era on Doctor Who, a slew of major characters from spinoff series' Torchwood and The Sarah Jane Adventures were enlisted into the ranks for a starry, action-packed sendoff against the Daleks. Arriving at the tail-end of season four the episode is wrought with enough nostalgia to give you the fuzzies.

Best moment: As over-the-top it is - and an obvious attempt to tug at the old heartstrings - it's got to be the part when everyone uses the TARDIS.