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Kaiba's reaction to the word "cooperation" is too over the top for its own good. Screenshots can be found here.
Yu-Gi-Oh subtitles often ruin the mood of serious scenes with Blind Idiot Translations that get the names of characters and cards wrong, use names from the dub, have bad spelling and grammar, or have other bizarre mistakes — for instance, having characters call Yugi "Mutou" in the subtitles when you can hear everyone call him by his given name). It's hard to take duels where lives are on the line seriously when you're busy counting all the errors in the translation.
Kaiba is called a seahorse in the sub because he really was called a seahorse. 'Seahorse' = 'young dragon'. It's a cultural thing, so it still qualifies as Narm; if you approach it from outside of Japanese culture, your first thought may be about ''male pregnancy''. There's no excuse for grammar or names, natch...
One sub translated a rather long sentence from Kaiba as "Power power power" - no punctuation.
When you think about it, that's how all of his sentences go.
There's also some occasional blatant swearing in said subs that come off as very much extremely out of character for the protagonists. It is very hard not to crack up when Yami Yugi calmly says to an opponent "F--- you" out of the blue.
In a late episode, the group encounters Yami Bakura in the Pharaoh's tomb. Yami Bakura causes a Duel Disk to materialize out of thin air and challenges them to a duel. Yugi shouts "He's got a duel disk!" in the same tone of voice other people would use to shout "He's got a bomb!" Even in this 'verse, that might be overreacting.
It's hard to take Pegasus seriously as a villain in the original Japanese version when he uses Gratuitous English in most of his lines - sometimes, almost the entire line.
"Welcome deeessu, Kaiba-boy."
The ending of the duel between Yami Yugi and Raphael. Yami Yugi's over the top "AIBOOOOOOOOOOOOOUUU!" is hard to take seriously, especially when there's rock music blaring in the background. Though many fans find it heartbreaking... or both.
After their rematch, while they are trying to leave the crumbling building, Yami yells "Raphael" 8 times consecutively.
The English dub of the Yami Bakura and Yami Marik duel. They keep going on about how they're going to send the other into the Shadow Realm. It's as if they were competing over who could be more evil.
The very fact that a card game is such serious business. It's one thing when it's tied to the mythology of the show, it's another thing when businessmen in their fifties challenge children to card games in order to seize a corporation.
While season 4 is generally rather narm-tastic, nothing beats the way Kaiba's plane is prevented from crashing: The dragon cards "react" to the danger, the dragons materialise, grab the plane and land it more or less safely.
Five words: Blue Eyes White Dragon Jet. In the manga, it's a regular jet with a paint-job, but in the anime, it actually looks like the monster.
Neo-Spacian Aqua Dolphin talking to Jaden... with just his head sticking out of the water.
The Yu-Gi-Oh franchise in general has a problem with doing things in the most overblown fashion possible when something subtler would have been more effective. One scene in Yu-Gi-Oh! 5Ds involves someone dying in a car accident because they weren't paying attention. Instead of simply crashing, they go over the edge of a cliff Thelma & Louise style and into the ocean below.
Dan Green once said in an interview that he used to push for less overblown Voice Acting because "if everything is at volume ten nothing stands out", but he was always just made to do the scene again.
Placido's transformation. Any seriousness is lost with his pose at the end.
Jack Atlas' response to Mina/Mikage confessing her feelings to him in the dub, proving that 4Kids had either no idea of how to handle romantic drama or no desire to do it properly:
Mina: Jack, I must admit, I have feelings for you... Jack: Of course you do, but we're talking about Carly right now!
Jack, despite being very tall and powerful-looking, was voiced by Ted Lewis in the English dub. Nothing wrong with that...except that Ted uses a similar voice for Jack as for Ryou Bakura. Seeing this overly-tall tough guy speaking in a genteel Australian accent is amusing, especially if you've gotten used to how Yu-Gi-Oh! The Abridged Seriesportrayshim.