Retraux Flashback

When a series does an Art Shift to an older presentation style for Flashback Effects to a time when it used this style. It may be in a work which has Art Evolution, calling back to its own specific past, or it may be a Affectionate Parody of more general styles.

When you have characters in a flashback appear the way they look in the story's present time, making their latest appearance a Retcon to the period of the flashback, it's Backported Development.

Anime and Manga

 * In the Sayonara, Zetsubou-sensei OVA, the art style for the ending animation shifts to the author, Koji Kumeta's original art style.

Comics

 * Marvel Comics will often use a style which approximates the old four-color style when presenting flashbacks to the stories originally presented in the 1960s-80s, or new stories which take place in that time frame. Additionally the characters who were around then will frequently be drawn in the style of Jack Kirby, the artist who drew most of them at that time (or Steve Ditko if it's a Spider-Man story).
 * The short Fanboy series drawn by ~Sergio Aragonés~ featured several art styles appropriate to the particular character(s) and eras being referenced in the story. One particular one was the cycling of the different styles and moods of Batman from his beginning in the '30s to the '90s.
 * In Supreme, all of Supreme's flashbacks to different eras feature era-appropriate art and storytelling. When harkening back to adventures that would have happened in the Golden or Silver age, he mentions how it seems so long ago and everything seemed so simple back then, accounting for the less detailed artwork and plain, no-nonsense dialogue.
 * Done for the Legion of Super-Heroes' 30th anniversary in 1988 where old LSH artists were used in flashbacks to old stories. (The 25th anniversary is more famous for using old LSH artists in nostalgia segments, but these segments were not flashbacks, but altenrate universes that diverged as of a particular era.)
 * The issue of Stormwatch where old superheroine Jenny Sparks reveals her history as "The Spirit of the 20th Century" has her flashbacks of each era drawn (and lettered) in the style of major comics of said era, such as The Spirit, Dan Dare, and Watchmen for the flashback to The Eighties. In a later issue, Bad Boss Henry Bendix's flashback of when he first found Rose Tatoo (The Spirit of Murder) was drawn a la Jack Kirby.
 * An issue of Secret Avengers had Black Widow travel back in time to save her teammates. One sequence set in the 1960s is told in an old newspaper serial format.
 * The stories in Deadpool: Flashbacks, which take place over 50-60 years' worth of Marvel Comics history, are all done in the styles of the artists (and time periods) being parodied, be it 1960s Jack Kirby or 1990s Rob Liefeld. The only exception to the treatment being Deadpool's speech bubbles, which are consistently modern in contrast to the various comic styles.

Film

 * The 2005 Taiwanese movie Three Times had three stories set in different time periods, all about the relationships between two character who were always played by Shu Qi and Chang Chen. The middle segment, set in 1911, is styled as a silent movie, with title cards and no audible dialogue.

Live Action TV

 * Pushing Daisies would do flashbacks to a sufficiently distant period (before the main characters' childhood) with the film style of that era.
 * Cold Case went nuts with this. Their tribute episode to Rocky Horror Picture Show brilliantly parodied the movie's style, color scheme, and...distinct acting style.

Newspaper Comics

 * The second panel of this 1995 Dilbert strip shows The Pointy-Haired Boss and Wally as they looked in 1990.

Video Games

 * The flashback case in Apollo Justice Ace Attorney uses the first game's graphics and music.
 * At one point in the Discworld II: Missing Presumed... computer game, Rincewind travels back in time to meet himself, just prior to the events of the first game. The past is an exact duplicate of the much more blocky sprites of the original.
 * The same effect appears in The Curse of Monkey Island, where Guybrush can peep out of a hole into a location from the first game before being chased back by an unseen "pack of stunningly-rendered rabid jaguars".
 * In Metal Gear Solid 4
 * Invoked hilariously in Space Quest 4 where Roger ends up traveling back to the first game. The whole place is rendered in EGA coloring and style.
 * The flashback dream sequence in Plok uses grayscale graphics, an old-fashioned font, piano music, and silent film-style title cards.
 * Using Ouroboros in the late, lamented City of Heroes/City of Villains to access a "flashback" mission started and ended the mission in sepia tone.

Web Comics

 * The Adventures of Dr. McNinja did this when Gordito told the story of how his father died: the comic, which had recently begun using shades of grey in the art, used the old flat black/white style.
 * Bob and George always presents the relevant timelines in that era's sprites (and occasionally backgrounds): "modern" day Megaman is 16-bit, Flash Back-era is 8-bit, and the far-flung future uses Mega Man X sprites.
 * In the commentaries for the The Order of the Stick print books, Rich Burlew has occasionally noted that going back to old styles (either for prequel segments, flashbacks, or bonus strips inserted into pre-Art Shift arcs) felt almost physically painful.
 * Pretty much the entire point behind Attack of the Super Wizards.
 * Subverted in Adventurers!: a flashback near the beginning of the final battle starts like this, but the character being narrated to complains.
 * Occurs in this Penny Arcade strip, as a flashback to a wager about Duke Nukem Forever coming out. Done again in this strip concerning Tech Marches On. Tycho comments in The Rant: "In my my mind, they have always looked like the first two panels."

Web Original

 * Whenever Red vs. Blue characters remember about something, it's shot in the same game as the season it happened in. For example, during Relocated when Sarge reminisces about all of the times Grif nearly died that were "worth it", it shifts from Halo to Halo 2 and back to the (then current) Halo 3.
 * Homestar Runner has occasionally had flashback sequences that use the art styles of the original children's book that the characters came from, or some other early part of the series' history.
 * Heta Oni plays with this trope. In flashbacks, the earlier style of artwork reappears; in previous time loops, the newer style appears.

Western Animation

 * On one House of Mouse short, flashbacks were done in black and white and with the characters drawn in the early-1930s circle-and-rubber-hose style.
 * A flashback in What's New, Scooby-Doo? that shows why Velma is afraid of clowns is done in the art style of A Pup Named Scooby-Doo.