These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anti-Climax Boss: What Team Catastrophe turned out to be, due to being Placido's Unwitting Pawns and not wanting to win as much as wanting to just break shit. Heck, Hans didn't even get to duel!
Ultimate Temporal Machine God Sephiron, Z-one's trump card, which can special summon as many of his Temporal Machine God monsters from his hand, Deck, or Graveyard, and turning their ATK into 4000 & Sephiron gains their combined ATK, but he destroyed at the moment he summoned because of Yusei's Ass Pull
Arc Fatigue: The WRGP/Arc Cradle arc again. It consumed two-thirds of the series, where its preceding arcs were around thirty episodes.
Ass Pull: This isYu-Gi-Oh!, so there's guaranteed to be a lot of come-from-behind victories revolving around cards that had never been foreshadowed. The most egregious example? Rubble King from episode 10, a card whose effect depends on there being a lot of cards in the Graveyard... and it just happened to be the second-to-last card in Yusei's deck. This card was created out of wholecloth to enable Yusei's victory in that episode and never appeared again, not even being released in real life. And technically speaking, he didn't need it in the first place; he could have activated his winning trap card, Blasting the Ruins, at the start of his opponent's next turn.
Badass Decay: Aki. At the start of the series, she was a cold stone bitch who nobody messed with or they would suffer from her unleashing the powers she had. Now she's a moe school girl who does almost nothing plot wise - until the WGRP, where she's racing and dueling with the whole team.
Jack suffered from this, too. While in the first season he was Yuusei's equally-matched rival and the secondary main character, he was the show's Plucky Comic Relief at worst and a Memetic Badass at best seemingly bearing no relevance to the plot whatsoever... Until a mini-arc actually addresses the perceived decay, with a robot duplicate of Jack's King persona claiming that the real Jack has lost his edge, saying that he cannot win against his past self. After losing once, Jack has a rematch and whoops his doppelganger's ass in spectacular fashion.
And just in case anyone still doubts Jack, another mini-arc saw Jack fighting against the forces of the forces of the Crimson Devil and stealing the powers of the Crimson Devil to make his newest trump card, Scar-Red Nova Dragon. It helps that he is the reincarnation of a legendary Signer with a special power called "Burning Soul"
The final episode pretty much turn him from emo self proclaimed covered by money king into a real king. He has some Magikarp Power on him really, going from Badass Decay into possibly the strongest among signer with only Yusei as the competitor.
Its funny to think that it is implied that without the Legendary Signer, the Crimson Dragon side is losing against the Scar-Red Nova. Now that same being is Jack's Slave/Trump Card. This implies that Jack is stronger than even the Crimson Dragon itself.
Base Breaker: Crow, Crow, Crow. Quite possibly the worst Base Breaker in the series, it's hard to find enough people who share opinions to come to a consensus on what they think he is and what he should be. Some people call him the Kamina of the series(Though most detractors say that the honor should go more to Jack). Others love him for what he is, the Large Ham of the cast. Still others call him a Canon Sue, citing his use of an archetype that's been a tournament staple in real life, the fact that he became a Signer, and the fact that he never shuts up as reason for being hated. This extends to just about any episode that revolves around Crow, to the point where, if you see Crow featuring prominently in an episode, there's bound to be an argument about it.
Broken Base: Let's just say that the only thing that the fandom can generally agree on is that the music is great and the first 64 episodes were better then what came after that. You'll have arguements on anything from how many seasons exist to correct character spellings to anything involving Aki and Crow.
Crashtown Arc - pointless filler that ran on for too long and changed absolutely nothing, or interesting arc focusing on a character that until now had been Put on a Bus? The fans may never agree.
As of Episode 107, Placido's transformation. The coolest villain in all of Yu-Gi-Oh!, or just silly?
ZONE's true identity, a good plot twist or poor writing after foreshadowing pointed to something else?
Canon Sue: Bruno is the most obvious example. In his very first episode he heavily outshines both Crow and Yuusei at D-wheel mechanics and computer hacking, beats Crow (an excellent duelist) and Jack (the former King of Games) at a duel puzzle after Yuusei (the current King of Games) asks him if it's even possible. Now subverted, since Bruno was secretly Dark Glass, Yuusei's watcher, albeit his memories seem to have gone the way of Laser-Guided Amnesia though he retained his great dueling prowess.
The jury is still out on whether or not Crow counts for this trope.
Kiryu also to a lesser extent. The fact that he ha obtained a seven episode long arc focused on him may or may not be acknowledging his fan popularity.
The Familiar of the Crimson Devil is quite popular as well, mainly due to his quirky personality.
Cup Ramen Man.
Carly prior to season 3.
Within the over-arcing franchise, Aki is one of the most popular female characters, not counting Duel Monsters. Like a major factor is that in contrast to prior females, she's a genuine Action Girl instead of a Faux Action Girl, just as competent in the duel arena as any of the males.
The whole of Team Taiyou, who were so utterly likeable that most fans ended up rooting for them in their match against 5Ds.
The show itself is this in the Yu-Gi-Oh! series lineup, due to invoking Rule of Cool, as well as being Darker and Edgier than the others. It also helps that the series immediately before and after are Broken Base shows at best, or seen as corny and childish at its worst.
Interestingly enough (and related to both of the above), in the 5Ds manga, it appears that Rex is Jack's father.
Zonesei/Oldsei. Yusei is ZONE The evidence fans use is stacking up in their favour. Jossed later on.
Sly is Divine's son.
Many people theorize that Yusei is now dead thanks to his final stunt shown of jumping over the bridge connecting Satellite and Neo Domino. It doesn't exactly help that Yusei already dodged huge air fans, jumped over a pit of magma and stood on top of a railling on a cliff in the final episode alone.
Rua/Aporia has quite the backing, especially once Aporia showed up to duel Z-one.
Jack's fangirls, Mikage, Carly and Stephanie.
Stardust Dragon and Red Demons Dragon. Most fight scenes between them are portrayed rather harshly, yet have no problem working together when necessary.
Fridge Brilliance: Some fans wondered why Yusei needed to find Accel Synchro when he already had Savior Star Dragon. But watching the Yusei vs. Placido duel, it becomes apparent that Placido had already found a way to counter Savior Star. Savior Star Dragon can negate ONE monster effect per turn, but stealing the Skiel Carrier cards gave Placido TWO lines of defense (Wisel Guard 3 and Skiel Carrier 5). Savior Star would negate one, bounce off of the other, and get absorbed the next turn. Game over, hero dead, town destroyed, roll credits.
Yusei's self blame towards Zero Reverse becomes horrifically justified when Yusei's future self is ZONE and Yliaster's leader. He was the one who guided Rudger into triggering the event, killing hundreds of people and his own father and causing what he feared the most.
Subverted in the fact it was merely someone who psyched himself into believing he was Yusei, made himself look exactly like Yusei, and then go mad from being unable to save the World from a Zero Reverse.
Fridge Logic: Quite literally. Crow was in one for around 24 hours! Indeed, this seems to keep happening to Crow as he, once again, avoided being killed by jumping into a fridge with an old man.
This bit is exclusive to the English Dub. If Jack, Yusei and Crow grew up together in the same neighborhood, from they were babies I might add, why is it only Jack has an Australian accent?
It's 4Kids. Leave it at that.
Yusei is looking for a card that can defeat the Emperors... preferably a Synchro Monster... a card that can ignore the effects of monsters (low-level ones, if that's important)... a card that fits into his Deck strategy, and preferably his Deck... Nope, ain't got nothing like that!
Genius Bonus: Similar to the many references to real-life subjects hidden in Yu-Gi-Oh! GX, the Fortune Cup and Dark Signers arcs are full of references to Incan mythology, while the W.R.G.P. arc gives us references to geneticists, genetics and biology.
Harsher in Hindsight: Luciano is nucking futs, a Laughing Mad child psycopath, and a Large Ham if there ever was one. But admittedly, it gets a bit hard to mock him for it after realizing he represents a child who was driven insane by the loss of his parents.
Straighter example: Zero Reverse and the Bad Future itself, thanks to Japan suffering what is pretty close to the real life equivalent with the 8.9 earthquake, tsunamis and power/nuclear plants exploding.
Hilarious in Hindsight: About a month and a half prior to the series airing, Yu-Gi-Oh! The Abridged Series had Tristan ride up on a motorcycle, and when asked he explained that "in the future, card games will be played on motorbikes," before cutting to a promotional artwork for 5Ds. Then the series got dubbed, and who should be voicing Yuusei but the same guy who voiced Tristan, using almost the same voice he did for Tristan too. Hilarity ensued.
Some fake episode titles mentioned something about a new Earthbound Immortal. With the airing of episode 112, we learn that the Crimson Devil is actually an Earthbound Immortal that fought one-on-one with the Crimson Dragon and lost.
Said immortal was based on a serpent Nazca Line, which wasn't known to exist at the time, but was later uncovered by a sandstorm.
Early in the series, a few people speculated that Power Tool Dragon might be a Signer Dragon as well. However, most fans were quick to point out the inconsistencies if such were to be true (such as being a machine type). It was also pointed out constantly in the show itself that Rua couldn't be a signer, a notable example being a recap episode in the WRGP story arc, also stating previous point. Cue Season 5, after the rumors were already dead a long time ago, where it turns out that Power Tool Dragon was actually a dormant form of the final original Signer Dragon, Life Stream Dragon, along with a new Signer mark introduced almost completely out of left field.
Hollywood Pudgy: Bruno, whose on-screen stats would indicate that he's probably closer to having a normal weight-to-height ratio compared to the rest of the cast, but because this is Yu-Gi-Oh!...
Incest Yay Shipping: Definitely YMMV but some fans see Leo/Rua and Luna/Ruka with this, particularly in one of the last episodes where Luna/Ruka is seen with a new look and Leo/Rua is blushing at the sight of that.
Nitro Warrior. Every single time it is summoned (except for the final duel with Jack), the opponent is OTK'd - in Crashtown, Yusei summons Nitro Warrior and OTKs three guys at once!
Jose. He runs down the track after Jack's D-Wheel when it's his turn to duel, and keeps up with him until he merges with his D-Wheel a few moments later. Many jokes ensued about the possibility of him just running around the track for the duel without a D-Wheel, which apparently he could have.
Memetic Molester: Aki - a lot of people make jokes about how her usage of Rose Tentacles on Yusei was a little too suggestive.
Akiza in the early seasons. There's even an ending in the Tag Force games where she makes plans to reward the player character for dueling alongside her by unleashing all of her power on them. While sporting a nightmarish grin◊ no less.
Crow may also qualify, being given a legitimate expanded backstory in 94 and 95.
The Scrappy: Who is a Scrappy in 5D's varies almost depending on who you ask. Crow is hated for being a Remember the New Guy character with a Game Breaker deck who "stole" third billing from Aki... that is, when Aki isn't being hated for going from Bad Ass crazy chick to Wangster to cheerleader. The twins are hated for being The Load and for providing what is seen as unnecessary comedy to a rather dark series, and even Yusei, the main character, has his haters, who claim he's a Invincible Hero with too much Incorruptible Pure Pureness. The things every fan seems to agree on, though, are that Jack, Carly, and most of the villains are awesome, and that Leo/Lyndon from episode 85 is an absolutely terrible character.
Seasonal Rot: Season Three (specifically the WRGP, before they go on to face the actual bad guys) tends to get a lot of flak for this.
Strawman Has a Point: While his plan to destroy an entire city was undoubtedly drastic, Zone is the last human survivor who was trying to prevent the same thing happening to the whole world. Team 5D's fights against his plan without even trying to think up of an alternative way to prevent the apocalypse besides a generic hope speech.
The Untwist: ZONE not being Yusei, despite sharing the same appearance and heavy foreshadowing.
They Wasted a Perfectly Good Plot: Jack's and Yuusei's scarred friendship was one of the main focuses of season one (and the entire focus for the first five episodes), but it was never fully explained what happened that caused them to grow so far apart after Kiryu's death.
A lot of Foreshadowing went into hinting at ZONE being Yusei from the future. When it was revealed he was just some random nobody who underwent plastic surgury to emulate Yusei, the fandom went nuclear.
When Sly, one of Rua and Ruka's classmate, was introduced, the series made notice that he had interest in Yusei's Stardust Dragon. This was never developed.
Aki's character arc in the second season began with her wanting to learn how to Turbo Duel to understand the adrenaline and energy that Yusei and other Turbo Duelists feel, and it was hinted she wanted to get closer to Yusei after being jealous of female Turbo Duelist Sherry. Once she got her license to ride Aki only ever took part in a single Turbo Duel as a member of Team 5Ds, and was eliminated in the same episode she went in.
Two episodes after she got Aki got her license, Rua and Ruka got a two-episode arc where they got to Turbo Duel using skateboards instead of motorcycles. This went absolutely nowhere.
After all the focus on Jack and Carly's relationship during the Dark Signers ark, the dreaded Reset Button rears its shiny head. Their relationship is never put into focus or developed in any form or shape again, and instead Carly is reduced to being just another Jack fangirl for the sake of comic relief. The sound you're hearing is the sound of Jack/Carly shippers reaching for the torches and pitchforks.
Divine and the Arkadia Movement in general reeked of wasted potential, especially since with the exception of Aki, Psychic Duelists were never really brought up again once they were gone.
Viewer Gender Confusion: Rally. Someone really needs to tell that kid that he dresses like a girl. The long fluffy hair doesn't help.
This is even lampshaded in Tag Force 4 when Carly tries to question Yusei about his life when Rally forces her and the player character into a duel. Carly whispers to herself, 'What is with this girl!? She's cute, I'll give her that, but...' to which Rally angrily responds, 'I'M NOT A GIRL!!!'. Carly completely ignores this and continues talking to herself about accepting the duel.
Jaeger fits the trope, too. Lampshaded in Episode 81, when a holographic Jaeger "clone" can't make up its mind whether it belongs in the men's or ladies' bathroom.
Luciano has a long braided ponytail, eyelashes and a feminine voice. But at least he wears the male school uniform.
Woolseyism: The English dub's "Earthbound Immortals" just sounds more dramatic than the original "Earthbound Gods". There's also a similar instance of renaming the Polar Gods to Aesir in the dub/TCG. Aesir is a group of gods that Odin and Thor belong to and which Loki is heavily associated with, despite not actually being one himself.
A notable instance is changing Himuro's knife that he hid from the prison guards into magazines. The dub simply makes it more subtle and turns it into a Parental Bonus.
Due to Never Say "Die", the dub couldn't bring up Misty's brother's death, so the conversation about Aki's powers in their first due changed from being about him to being about Aki's actions at the Fortune Cup. The Woolseyism part comes from Misty's Armor-Piercing Question of whether the crowd deserved to get hurt for mocking Aki and whether she actually just enjoyed inflicting pain. Her stunned inability to answer just emphasizes how powerful that question was.
Dark Signer Bommer in 2010. A riding duel is painful enough since the game introduces it not long beforehand and you must allow him to summon his Earthbound God in order to win.
Dark Signer Kiryu from the same game could count as well the first time you face him in story mode. Facing a boss playing an Infernity deck when both players start with no cards in hand could be a nasty challenge for the unprepared.
Dear god, Lawton in 2011. He starts with 10 cards in his hand and runs pure burn. Do the math. Sometimes you need a miracle not to be killed on the first turn.
That One Level: The stealth missions of sneaking past Security. This was a pain to complete in 2009 and they mercifully toned it down in 2010.
The "battle" against the Ghosts in Over the Nexus thanks to an Unexpected Genre Change to Bullet Hell. Better hope you've been keeping up with your D-Wheeler parts, because without a decent amount of health and good maneuvering ability you will be destroyed and have to start over.