Often (immediately) followed with "...where X and Y collide"
This page lists several examples real-life "in a world" trailers, most of which are non-parodies and most of which are by Don Lafontaine, though few actually begin with the phrase in question. This is just to officially prove, if such proof be needed, that the "in a world" trope is not a Dead Unicorn Trope.
An increasingly frantic soundtrack for action/adventure movies, abruptly silencing for a character to make an ironic remark, then finishing with one last BUM-BUM-BUM BUMM!!!
A fairly recent addition has been the use of whooshes (as in sound effects) and plenty of them, usually punctuating cuts from scene to scene or scenery pans. Expect on occasion a boom hit to mix things up.
The trailer for the Star Trek film Into Darkness is punctuated by nothing but booms.
Chanting or cheering (often gradually increasing in volume as a fade-in happens). Especially common for sports movies.
Montage increases in speed as the trailer progresses, until what you get is a succession of one-second shots, often followed by a Fade to Black, and then the movie title.
Whatever the movie's actual soundtrack is, the trailer's own soundtrack will be Carmina Burana, Lux Aeterna or scratchy, tension-filled electronic music.
Unless it's a sequel, in which case it will usually use the first film's soundtrack.
Or a guitar-heavy rock song that doesn't appear on the soundtrack playing over action-packed, fast-cut footage from the movie. This is usually done in TV commercials for the movie instead of the full trailer.
"(Coming) this year/summer/fall/winter/soon (to a (movie) theatre near you)"
This has since been condensed to simply 'This summer/fall/July/whathaveyou'; in particularly poisonous cases, this is followed several cuts later by an exhortation for the audience to PUNCH CRIME or otherwise do something that the characters in the film will be doing (rather than, more sincerely, exhorting them to purchase a ticket and see their film) They may also be asked to go on an adventure "beyond imagination", or beyond something similar. This was perhaps a fair cop in Zardoz's advertising campaign (well, it was in keeping with the lunatic bombast of the film, at least), but when attributed to the Mummy films, it just looks desperate.
The trailer often ends in a shot of the movie's title; it may or may not be spoken by the narrator.
If the title shot isn't the end, there'll be The Stinger with a particularly cool or funny moment from the movie.
For suspense pictures, the title shot may be accompanied by a particularly chilling line from the film.
The suggestion that "If you only see one movie this summer/fall/winter/spring, make it..." A Dead Horse Trope now seen only in subversion.
"All [character, often a child] ever wanted was..."
"From the creators/producers/director of (movie title) comes a story..."
Starring [Academy Award winner/nominee] X, [Academy Award winner/nominee] Y, [Academy Award winner/nominee] Z...
"If you liked (title), you'll love (other title)."
Sometimes seen in remakes, or sequels of really old moves (Often promising the Duke Nukem effect), Several dark, quiet, or shaky camera shots, followed by a very quick glimpse of something recognizable from the previous film.
The best example would be the Star Trek movie (2009) teaser, where you couldn't see much, until the last shot showed that it was the Enterprise.
The "trailer" at the end of Kung Pow!: Enter the Fist was just scenes cut from the film along with this kind of narration.
The trailer for Austin Powers: The Spy Who Shagged Me, which came out the same summer as Star Wars Episode I, after doing a fake out bit about Star Wars, had the narrator say, "If you only see one movie this year... make it Star Wars. But, if you see two movies this year..."
In The Holiday, Cameron Diaz's character Amanda works in Hollywood editing movie trailers, and even when she gets away on vacation a voice in her head (Hal Douglas!) sometimes reflexively narrates her emotional ups and downs using trailer-voiceover-speak, laden with this trope. The whole movie has numerous affectionate shout-outs to the film industry.
Done straight and with a twist in the trailer for Heavenly Creatures: "In a world where dreamers and believers are miraculously transformed..." "But ours is not a world that believes in magic..."
In a world of wealth and privilege, he was an outsider ...
In Moving Pictures, the standard phrase is "Against The Backdrop Of A World Gone Mad!" At one point Soll is attempting to negotiate with a group of dwarfs who object to being stereotyped as miners ("But most dwarfs are miners!" "Yes, but we're not happy about it."), a troll who wants to play the leading man, and various other people nitpicking the plot, when someone asks him why all Mr Dibbler's pictures are set against the backdrop of a world gone mad. His response is "Because Mr Dibbler is a very observant person."
On the pilot for Frank Caliendo's short-lived show, Frank TV, there is a segment parodying the Three Tenors where three movie announcers go on tour. It guest stars Pablo Francisco and Don La Fontaine, and begins, "In a world..."
Homestar Runner spoofed this repeatedly in the Strong Bad Email narrator, where Strong Bad went around narrating the everyday lives of his friends and neighbors as if they were movie trailers: an argument between Bubs and Coach Z over napkins becomes a trailer for a post-apocalyptic action film, a tiff between Marzipan and Homestar over a goofy novelty chef's hat becomes a trailer for a romantic dramedy, the Poopsmith shoveling... whatsit becomes a trailer for a snooty French art film, and Strong Mad and The Cheat playing Battleship becomes a trailer for a buddy comedy. Butt Monkey Strong Sad is "fortunate" enough to get two trailers: one for a comedy where he gets hit in the face with an octopus, and one for a horror movie where he gets hit in the face with a dead Canada goose.
Here Comes Dr. Tran revolves around a five year-old boy getting harassed by a movie trailer narrator.
Narrator:He...is a man of action... He...is a man of honor... Tran: Who is that? Narrator:He...is a man of duty... Tran: Are you talking to me?
Well, it was only a matter of time before someone started making theater-style commercials for webcomics. Since the comic in question is The Adventures of Dr. McNinja, saying 'in a world where anything can happen' is rather an understatement. May be viewed here.
This piece of narration form Roommates (Here) which is also the current page quote for it: "Somewhere, there is a place where all stories are real and all dreams are truth..." but it also promptly subverts/parodies the trope "...This is not that place..." just to make it a double subversion at the end "...This is not quite that place, but it's close."
All the movie ads in the commercial breaks while the Whateley Universe characters are watching "Tales of the MCO", including ads for Oliver Stone's "Foucault's Pendulum" and the Merchant-Ivory production of "Hulk 1809".
South Park episode, "The Biggest Douche in the Universe": While the boys are on a flight to Chef's parents' house to release Kenny's soul from Cartman's body, they are subjected to a handful of trailers for Rob Schneider movies, most modeled after roles he played in The Animal and The Hot Chick, and given similarly ridiculous titles such as ''Rob Schneider is...A STAPLER!" and "A CARROT!" One particularly ridiculous trailer starts out like this:
The later episode "Stanley's Cup" takes it even further. Stan is forced to coach a Peewee hockey team to pay off a ticket, living out many Sports Movie tropes in the process. Meanwhile, the court clerk is following him around with a record player, narrating everything he does in the In a World voice.
In a tragically hard-to-find-online clip, the Foster's Home for Imaginary Friends episode "One False Movie" climaxes with the Ninja Pirate Zombie Robot opening of Bloo and Mac's Colon Cancer-patient film, which appears to be a trailer for itself. "In a world where chaos reigns like cats and dogs in a hailstorm of... passion, a retired cop must settle one last score. [Against ninja.]"
A trailer for Brother Bear starring a moose where the moose and his friend narrated the trailer. It begin with, "If you only see one movie this year-" "Wait, hold on, if they only see one movie, wouldn't it be the movie they're watching right now?" And then a plea to stop watching the current movie and then watch their movie... or just watch two movies this year.
Then subverted by LaFontaine himself: "In a world...there, I said it. Happy?"
Played straight (well, sort of) on Fillmore! when they have the man himself do the opening voice-over for every episode and every "chapter."
In the DVD Commentary for Hoodwinked, the creators mention how trailers always seem to start with the phrase "IN A WORLD..." They go on to joke that all they know about the planned sequel to their movie is that it will take place "IN A WORLD."
Parodied in Johnny Test. Susan and Mary build a machine that allows people to warp reality by beginning a sentence with "In a World..." and speaking into it. Things get way out of hand.
Home Movies incorporated this in Brendon's first movie ever shown on the show, Dark Side of the Law: "In a world gone mad, there stands one cop fighting against evil and injustice!".
American Dad!: Spoofed by a drunk Roger, complete with a mock dramatic voice.
Roger: In a world where vomit comes out of my mouth...(throws up)
Frequently parodied by British film critic Mark Kermode, eg "in a world of queens, she was her majesty..."
And now for the trailer for Benjamin Sniddlegrass and the Cauldron of Penguins:
"In a world in which narrative coherence is under threat, it takes a real hero not to lose the plot, and in a world in which holding onto a penguin can mean holding onto the woman you love, one boy better make sure he doesn't lose the plot."