Mind Screwdriver

"HAL: I'm evil. (kills astronauts) Dave Bowman: I must shut you down now, HAL. HAL: Daisy, Daisy... Dave Bowman: Now I must finish this mission alone. (STRANGE THINGS happen, and they MAKE SENSE.) Reader: Wow. I understand the movie now."

- RinkWorks condensation of the novel version of 2001: A Space Odyssey.

A Mind Screwdriver is a side-story, sequel, or piece of bonus/AllThereInTheManual material that exists at least partially for the purpose of clearing up a Mind Screw and/or Gainax Ending. When done well (and presented in such a way that viewers can easily find it), a Mind Screwdriver can make an already interesting plot that much more so, and even add a new layer of depth to the story. When done poorly, it can feel like a rather lame cop-out by writers who didn't care enough to solve the problems (continuity-related or otherwise) that their additional information created.

Chances are very, very good this never made it out of the country of origin.

Anime & Manga

 * Higurashi no Naku Koro Ni Kai: Abandoned the "nice kids in rural Japanese town go nuts and start killing each other" premise in order to clear up the Mind Screw of the first season in its entirety.
 * Advent Children pretty much exists entirely to clear up the Mind Screw at the end of Final Fantasy VII. Or at least assure the world that they hadn't intended the ending to be a Kill'Em All.
 * Better candidates for the Mind Screwdrivers of Final Fantasy VII and its Compilation are the Japan-only Ultimania books which do explain a number of plot points and answer many long-asked questions.
 * The End of Evangelion was supposed to clear up the lingering questions left behind by the notorious series ending. Of course, Evangelion wouldn't be Evangelion without rampant trope subversion, so the movie managed to clarify some things about the plot while still leaving massive questions unanswered, introducing whole new ones, and being a complete and unmitigated Mind Screw in and of itself.
 * The DVD commentary for FLCL clears some things up.

Comicbooks

 * The introduction of the Graphic Novel version of the (deservedly) obscure comic book sequel to The Prisoner rationalized away the last episode in a particularly unimaginative way.
 * The tie-in Graphic Novels for Heroes qualify; they usually take place as side-stories complimenting the concurrent episodes (helping to make sense of different viewpoints in the story), and also offer glimpses into the pasts and minds of various characters (helping to make sense of them and the Heroes-verse in general).
 * Up until they're RetConned by later comics or the series itself. Happens enough that they have next to no weight in canon.

Fan Fiction

 * Thousand Shinji delivers a Lampshade Hanging/Take That to the Mind Screw of the original Neon Genesis Evangelion: "For those of you prepared to rant at me, there is one more chapter to this story, so unlike Gainax, you will actually get an explaination (sic) as part of the denouement." It then proceeds to do just that, having  explain what looked like a Gainax Ending.

Films

 * Much of the film 2010: The Year We Make Contact is devoted to explaining the ambiguities of its predecessor, 2001: A Space Odyssey, particularly why and just what happened in the trippy ending sequence. Or you could just read the novels.
 * There were intended to be releases of these for Southland Tales, but they never appeared. Just as well, because trying to make sense out of that movie would probably take out at least one forest.
 * You can in fact purchase them on Amazon.com right now. It has a release date of July 11, 2006 which is well ahead of the movies US release of November 14, 2007.
 * Southland Tales, for many viewers, suffers from being so ambitious that they're not willing to decipher it. While the books (the movie's only part 4-6; 1-3 are a graphic novel) do fill in lots of backstory, online director interviews and other breakdowns are quite helpful in clarifying the deep, yet admittedly confusing, film.
 * Donnie Darko has the eponymous character who receives a book on time travel from his science teacher, time traveling also being the central plot driving device of the movie. A director's cut released a few years after the original DVD release briefly cuts to pages from said book, where the mechanics of time travel in this movie are explained - which is vital to figuring out what the hell is going on.
 * The book was later actually published and released. It explains most of the background and events present in the movie.
 * Several small scenes during the credits of Wild Things piece together the otherwise incomprehensible series of twists and turns the story takes.
 * Memento's plot makes sense on its own (as long as you can keep up with it), but the website gives an awful lot of backstory (including spoilers) that lend a much fuller understanding.

Literature

 * The Book of Lost Memories was written to explain the mountains of symbolism (but not the plot) in the first three Silent Hill games. Whether this lessens the ambiguity or makes an already Mind Screwy series even more impenetrable is still up for debate.
 * The Xenogears Perfect Works books provides backstory and detailed exposition necessary to understand a game so choked with symbolism and Mind Screws.

Live-Action TV

 * Bruce Kalish had to explain a good deal of Power Rangers SPD's plotholes in interviews after the fact. Also, the official website explained that A-Squad had been brainwashed (as opposed to the improbable apparent scenario in-show: the whole team deciding to go bad.)
 * The final season of Lost seems to be shaping up to be this. It's about time...
 * ...in more ways than one. You know, since so much time travel is involved.
 * It both succeeded and/or failed spectacularly. Fans are divided.
 * The season six DVD's contain an epilogue which explains a whole lot of the remaining mysteries.
 * The online material for Smallville often clears up some of the backgrounds and relationships of certain groups and characters, like the history of Smallville and how it connects to Krypton, or the Veritas society.
 * The Grand Finale of Ashes to Ashes impressively managed to be one of these for not just Ashes but its parent series Life On Mars.

Music

 * The story that Peter Gabriel wrote for the liner notes of the Genesis Concept Album The Lamb Lies Down on Broadway.
 * It actually doesn't explain things that well. For that, see this site. And prepare to walk away still not sure...

Videogames

 * The World Ends With You: The Secret Reports. Of course, getting them all unlocks The Stinger, which is more confusing than anything in the actual plot.
 * Similarly, the Ansem Reports in the Kingdom Hearts game, by the same people.
 * Kingdom Hearts: Birth By Sleep is also a Mind Screwdriver, filling most of the holes left by its predecessors.....of course, only to set up plot elements that evolve into an even bigger Mind Screw in the next entry of the series, Kingdom Hearts 3D.
 * Metal Gear Solid 4 managed to clear up the plot of MGS2, at the price of creating a truly spectacular Continuity Lock Out and Doing in the Wizard.
 * Speaking of MGS2, the game was going to contain a Mind Screwdriver of its own in the form of Psycho Mantis' mask as an unlockable. It was going to let you hear the thoughts of other characters during cutscenes/codec calls, and those thoughts were supposedly going to give you a major clue to what was really going on in the game's plot. But alas, the game was rushed for the holidays, so it didn't get implemented.
 * The Umbrella Chronicles is a retelling of several games in the Resident Evil series which attempts to fill in the plot holes the previous games left behind. (Resident Evil: Code Veronica featured a video, on a bonus disc, which tried to do the same; "The Wesker Report" was subsequently made obsolete when the next games retconned the story in a different way.)
 * And Resident Evil 5 had a nice Author's Saving Throw, though it might be a Voodoo Shark, explaining what was up with how Wesker got better, one of the main parts that was kept.
 * The game version of I Have No Mouth, and I Must Scream was made to further flesh out the characters in the original story as well as answer the question as to why AM was doing what it was.
 * The "True Ending" of Ever 17 clears up just about every mystery in the game. And some things that weren't, but were probably misinterpreted.
 * The Once Upon A Time chapter that shows up at the end of Rule of Rose is one of these, if you get the good ending.
 * Trilby's Notes, of the Chzo Mythos,ended with the title character being saved by an unknown man in red. The identity of this man was not revealed until the ending of the next game, and it was a mind screw. It also explains how the man was able to revive Trilby.
 * The Special Edition versions of the games (especially 6 Days) provide a few other Screwdrivers as well, most notably
 * Assassin's Creed Revelations is the screwdriver for the Assassin's Creed series up to that point, explaining what happened at the end of Brotherhood as well as revealing more about . Of course, there are still mysteries to be solved by Assassin's Creed III...
 * Hand in Killer7 was supposed to be this, but because it was made before the game was finished, some of the material in it wasn't used in the game. So, while reading Hand in Killer7 makes sense of some of the plot, it makes the rest of it even more mind screwy.

Webcomics

 * Homestuck's three Recap Episodes (and similarly, the two Problem Sleuth recaps) are an invaluable aid to those who find themselves lost in the Kudzu Plot. Andrew Hussie's Formspring and the MSPA forums are also pretty handy references for clearing up ambiguous plot points.

Web Originals

 * Red vs. Blue: Recreation and Revelation serve to explain a large amount of the more wacky elements of previous seasons, most noticeably the "time travel" incident in Season 3 and any point in the series where a character died and got back up again.

Western Animation

 * Adventure Time had a season one episode "Tree Trunks" where the titular elephant bit into the crystal apple she was looking for so she could bake an apple pie out of it. She exploded, and then was seen giggling and laughing through the apple. End Episode. Season two had a followup, "Crystals Have Power" where she went insane, became queen of the crystal realm, and tried to turn Finn into her Crystal King. Jake punched the crystal chunk out of her and she returned home to bake them another apple pie.