The number of Crystal Cards required for a Crystal Star increases from 7 to 8.
Redux does not use the "Fusion Monsters cannot attack the turn they are Fusion Summoned" rule.
Duel Spirits now give out Crystal Cards upon defeat in Redux.
The animals living in the island have been replaced with Duel Monsters.
In the chapter where in Fran duels the Unfriendly Amazon, her nightmare changes from a duel with Seto Kaiba to a duel with Jackson; who has Raviel, Lord of Phantasms.
There are a few duels that were included in between some duels from the original version. Either to replace the ones removed or as expansions of the story.
There is now an added duel between Andy and Smithy that takes place between Stan and Francesca's tag duel in Gearville and Andy's duel with Chico.
There is also an added duel between Merlow (Merlee in the original) and the Shadow Queen that takes place between between Andy's duel with Chico and Fran's duel with Maria.
The Shadow Queen finds out about Merlow a lot earlier in Redux.
Which leads her to confronting him personally, something she never did in the original.
In Redux, At the end of the chapter where in Fran duels Kyle, there is an added scene where in Kyle catches Jackson spying on her. He then duels Jackson, who he defeats at the start of the following chapter. Afterwards the Witty Phantom appears and gives Jackson the deal.
Rawk Hawk does not willingly work for the Shadow Queen in Redux compared to the original version, and in fact, is a part of a group that opposes her.
The Shadow Queen's origin is completely different in Redux, and she has a different real name. In the original fic, her name was Josephine, while in Redux it is Iris.
The demon that she made a pact with in the version was left entirely unamed. In Redux, this was changed to be the demon lord Graz'zt.
Stan, Fran and Andy also learn more about her origins a lot earlier in Redux.
In Redux, the Shadow Spawn (minus Vladimir) do not attack Stan, Fran and Andy upon their arrival at the Thousand-Year Door.
The puzzle the Witty Phantom puts Stan, Fran, and Andy through is completely different in Redux. In the original it involved numbers, in Redux it involved finding his door based on a code.
The Shadow Queen is more lenient to Crump after he steals from her and disobeys her orders by dueling Stan (because Grodus reminds her that he has an important fuction, that could only be done by Grodus himself if she got rid of him).
In the confrontation with the brainwashed Diana, Diana duels Andy instead of Stan.
In Redux, the Shadow Queen does not make her children train against holograms of Yugi, Jonouchi and Kaiba. Instead she lectures them on how mistakes can cost them a duel.
The concept of Soul Cards and the Seven Sins in regards to the Shadow Queen and the Shadow Spawn are completely absent in Redux.
In Redux it is known that there used to be another set of Shadow Spawn, who were the Queen's original heirs. According to Kurtis, their mother always considered them a lot more capable than the current Spawn are and always reminds them of it. Only two of them are known: Damian, the original Shadow Spawn of Darkness and an unnamed female who was the original Shadow Spawn of Fire, whom Tyson seems to look up to.
During the duel between Stan and Vladimir in the original version, Vladimir forgoes a move that would've countered Stan's as he refuses to continue serving his mother. In Redux, Count Bleck ends the duel prematurely to thank Stan, Francesca and Andy on how they helped him drive attention away from the Queen and to tell them that their alliance is over, then leaves with Vladimir in tow.
He also sends three of his minions to challenge Stan, Andy and Francesca in order to stall for time until the Queen arrives.
Grodus duels much later in Redux compared to the original version. In the original version, he dueled Andy sometime before the rematches with the Shadow Spawn began. In Redux, he (along with Crump) duel Andy and Francesca after the Spawn rematches and after the Queen kills Count Bleck, in order to buy her some time.
Andy and Grodus' duel also happens a lot later, taking place in the penultimate chapter of Redux. Also, the circumstances wherein the two are dueling are a lot more intense than in the original version.
The origin of spell that causes the Shadow Spawn to fuse into Elemental Mistress Doraido is different in both versions:
In the original version: The Queen casts an Amalgam Spell that transfers their souls into Doraido in order to combat Stan, Andy and Francesca one last time before the finals began.
In ''Redux', the Shadow Spawn had developed the spell themselves behind their mother's back and use it to oppose her until she makes a bargain with them, causing them to confront the protagonists one last time.
In Stan's rematch with Raven in Redux, Raven loses to Stan fairly instead of a grave error on her part in using one of the Companions in the original version.
The other finalists also discover the Queen's true nature a lot earlier compared to the original.
In Redux, there is also a subplot about the Arcadian Parliament that involves the resistance group.
Which later results in Pennington and Rawk Hawk doing a rescue mission to rescue the captured Cindy, Sean and Jose.
Kyle's duel with Drake in Redux ends in a draw as a part of their ploy to pull a monkey wrench in the Queen's plans compared to Kyle simply winning against Drake in the original version.
Kyle doesn't confront the Queen himself before the finals compared to the original version. Instead, he and Drake observe the confrontation between the Queen, Lyrius, Grodus against Lan'tao and a brainwashed Rave.
As a result of this, the Queen gives them a chance to escape the island, only for the two to change their minds later on to support the heroes. Nonetheless this disqualifies them both from the tournament leading to the Triangle duel, instead of Kyle being imprisoned by the Queen in the original version and her claiming he was disqualified for supposedly trying to sabotage the other's decks. Which means he witnesses the upcoming final battles in Redux.
In Redux, there is also another subplot involving Hyde traveling to the Queen's prison due to Merlow's request to discover what she's possibly hiding in the 9th level.
In this subplot, he runs into Rave, meaning this subplot possibly explains how she came to join the Backwater Shadowchasers.
The Queen's intended final fate for the protagonists is completely different in Redux. In the original version, she planned to extinguish their souls using the Soul Release card. But in Redux, she plans to go for a public execution with the help of a Warrior of Tradition Duel Spirit (which is actually a lot more merciful compared to the original version.)
In the final battle against the Queen. Stan and Francesca do not mix Andy's cards with their own. Instead, they receive a card from Drake and Kyle respectively. However, they do receive a few of Andy's key cards and a few powerful new ones via Falagar's magic.
Also, Lyrius participates as the Queen's tag partner, making the final battle a tag duel in the process.
Some character traits have been removed or changed.
Stan does not seem to be a fanboy of Yugi Muto in Redux compared to the original fic and as a result doesn't call himself his "apprentice".
His uncle, the one who gave him most of his cards also changes from a judge in the original, to a head of an correctional institution in Redux.
Francesca's ancestor changes from a warrior princess in the original, to a unicorn maiden in Redux.
In Redux, she also has a fear of Ojama monsters.
Diana does not seem to be a fan of Green Lantern in Redux. Instead her favorite superhero is Wonder Woman.
Because she uses a different deck (and that Seto Kaiba is probably dead), Melissa does not have the dream of owning Seto Kaiba's 3 Blue-Eyes White Dragon cards.
Kurtis does not seem to be as lustful as he was in the original fic.
Tyson's habit of comparing people and situations with others is replaced with making bad jokes every so often.
Leopold no longer has the habit of making calculations in everything and anything that happens.
Later on in the Palace of Shadow, he no longer uses his Mesmeric Control card to make the protagonists hallucinate that they lost their duels with the previous Spawn.
The Shadow Spawn in general come off as more sympathetic and less antagonistic towards the protagonists during the rematches in Redux. In the original, they challenge the three of them to Shadow Games while in Redux they don't (they also don't seem to have the ability to create them either.) Also in Redux, it is made more clear that they are also their mother's victims as much as the rest of Arcadia are.
The characters of Wanda Underwood, Jeff Azure, Lyn Rykern, Ushio, Cyrus Gamule, and Gerald Laxina do not appear at all in Redux.
Because Wanda was a finalist in the original fic, that position is given to Aesop instead.
In their place, are new characters such as: Jose, Cindy and Hyde Vayne (who originates from author Lux-Nero's Shadowchaser stories).
In Redux, Raven's real name turns out to be Lidia Sinclair.
She also comes off as less nasty compared to the original version.
Also in Redux, it appears that she and Drake have some sort of "thing" going on since they reached the center of the Palace if comments from other characters are to go by.
Noah Kaiba doesn't appear at all in Redux. Instead his name is mentioned casually by the Witty Phantom when the protagonists first arrive in the Palace of Shadow.
The backgrounds of the Companions are expanded a little - or in a lot in Vivian's case, where Lyrius was her informal mentor. It is also explained how their spirits became sealed in cards.
Some characters have had their names changed in Redux.
The character that was called "Merlee" in the original is now called "Merlow". (Done because Merlee was actually a female character in the game.)
In Redux, it is also revealed that his real name is Adrian.
Merlow's backstory also changes from the sole survivor of a group of people that the Queen had exterminated, to the son of Artorigus, a knight who had opposed the Queen in the past.
The character that was called "Yumi" in the original is now called "Yuki" (done to avoid confusion with another character named Yumi in another of Occam Razor's fics.)
The man who took Raven in when she was young was named Sticks in the original. In Redux, his name has been changed to Faustus.
Marv the Mad Magician is now referred to as Mad Jack.
Colette, Stan's girlfriend, is now named Christie.
Count Bleck is included in Redux as Stan, Francesca and Andy's supporter inside the Palace of Shadow, taking the role from Merlow in the original as well as replacing Noah as the one who created the Deckmaster system in the Palace. He also has some mysterious agenda that involves Vladimir. Although later on it is revealed that he was only using the three protagonists in order to advance his own agenda regarding the Shadow Queen and rescue Vladimir.
Later on it is revealed that he is Vladimir's father as well as the Queen's original consort.
Merlow is now a leader of a secret resistance in Redux that aims to defeat the Queen's forces outside the Palace of Shadow. Although later on, he resumes his role in the Palace of Shadow shortly after Count Bleck's death.
Characters like Ryo, Sean, and Yuki are also a part of the resistance, compared to the original version wherein they ceased to play a role in the fic after their initial duels. Aside from them, Jose, Cindy and Hyde are also a part of the resistance.
A new character named Lyrius is also included as the Queen's Shadow who plays a large role in the Queen's new backstory.
For Duel Spirits
End of Anubis and Peten the Dark Clown in the original fic have been replaced by Chaos Hunter and Saggi the Dark Clown respectively.
The Unfriendly Amazon while also appearing in Redux, has a smaller role compared to the original, and she is never seen again after her 1st and only duel with Francesca.
Infernalqueen Archfiend is replaced by Junk Warrior as the Duel Spirit sent by the Queen to test Kyle.
She makes an appearance later on in Redux alongside several other Archfiends in challenging the resistance force during the Arcadian Parliament subplot.
Freed the Matchless General is replaced by Sea Serpent Warrior of Darkness
The Witty Phantom has a much larger role in Redux than in the original fic.
Magical Scientist is also included as the one who works on Smithy's blueprints in order to create Dark cards for the Queen to use.
Ruklamba the Spirit King takes the role of the Unfriendly Amazon as the Duel Spirit with a vendetta against Francesca.
Scab-Scar Knight, Nurse Reficule the Fallen One, and Prophecy Destroyer are included as Bleck's minions.
Rave and Lan'tao from Shadowchasers: Twice-Told Tales also make an appearance. The latter being responsible for killing Lyrius several centuries ago. While the former is a major protagonist in 7th Librarian's fics.
Falgar, a new character who served as the The Mentor of the original Three Heroes is also included in the penultimate chapter of Redux.
Because of the change in setting, a lot of old cards are considered well-known already instead of being new back in the original.
Most of the effects of the Companions and Enchanted Cards have been changed, some with only minor adjustments, some with completely different effects.
Showstopper and Supernova have turned from Trap cards to Spell cards.
Among the companions, Yoshi and Ms. Mowz switch partners.
Yoshi: Fran - original, Stan - Redux
Ms. Mowz: Stan - original, Fran - Redux
Servants of the Shadow Queen can now use the Enchanted Cards in Redux compared to them being completely ineffective in the original fic. But instead, there are placed with a curse that would mostly assure that they would lose.
A lot of the character's decks have been completely changed. Here is a list of known changes:
Stan: Dark Magician -> Xyzs with primary focus on the Gagaga and Djinn Xyz archetypes.
Francesca: Amazoness -> Unicorn Synchro
Andy: Unchanged but seems to focus more on Dragon-Types themselves rather than dragon-like monsters. He also puts more emphasis on Dragon Fusions.
Melissa: Light Beatdown -> Lightsworns and later Lightrays.
Kurtis: Unchanged, but he now adds a few Dark Winged-Beasts led by a Dark Simorgh during the 1st duel. Later on, during his 2nd duel, he changes from a Standard WIND deck in the original to a more focused Harpie Deck in Redux.
Tyson: Unchanged (although Volcano Assassin is now an Xyz Monster instead of a Fusion Monster) in both duels.
Leopold: Dinosaurs -> Plants, then later during his 2nd duel: Beast-Warriors -> Gem-Knights
Maria: Unchanged, then later during her second duel: standard Water/Ice -> Ghost Pirates
Vladimir: Skull Servants -> Steelswarm, then later during his 2nd duel: Fiends and Spellcasters -> Zombie Counterpart
Shadow Spawn United (Gestalt Form): Unchanged
Jackson: Unchanged, but later during his rematch with Fran he changes from a deck focusing on Megarock Dragon to a Rock Special-Summoning Burn Deck.
Poison: Standard Fiends -> Heavy Industry, and later a Standard Machine Deck.
Ryo: Standard Fiends -> Goblins
Raven: Dark Scorpions -> Blackwings (mostly those used in the manga)
Sean: Mostly unchanged, but no longer uses Destiny Board and Dark Sanctuary turning his deck from an Occult deck to a Standard Fiend deck.
Diana: Elemental HERO -> Heroics, later uses a Destiny HERO deck when brainwashed by the Shadow Queen.
Kyle: Unchanged, later on uses a Chronomaly Deck during the finals in Redux.
Aesop: Gate Guardian -> Fabled, also owns a Mermail Deck
Cortez: Standard Zombies -> Ghost Pirates
Merlow: Human Wave -> Normal Warrior, and later a Gemini Warrior/Noble Knight Deck
Mad Jack: Toons -> Big Top
Shadow Queen: Archfiends, Red-Eyes and Divinity -> Fanatic/Contantoce, Smithy Gang, Sister Ritual. She also used a Terror Villain deck in Twice-Told Tales.
Crump: XYZ Machines/Vehichroids -> Machine Trains, and later a Gimmick Puppet Deck
Grodus: Dark World -> Company of Malice
The Unfriendly Amazon: unchanged
Rose Spectre of Dunn: Standard Plant -> Plant Fallen Angel
Agent of Judgment - Saturn: Standard Fairies -> Hieratic