That is NOT HOW SECURITY CAMERAS WORK.
We don’t see Pegasus for the duration of the double duel in the manga, so basically any time we see Pegasus just sitting around watching the duelists is all anime filler (see: Episode 10).
Anime Kaiba continues to pretend he’s Batman, sneaking around with Hair Guy, lurking in the castle’s dungeon, trying to bust out Mokuba. Of course, the raises the question of what the heck he was doing since he arrived on the island. He got there in the middle of the night, and it’s full daylight by the time he gets to the castle. Did he just wander around the island for like six hours? Did he take a nap?
Manga Kaiba also got there in the middle of the night, but he makes it into the castle while it’s still night, and he…
Either way, Pegasus shows off that Mokuba is locked up in his dungeon. Anime Pegasus greets Kaiba in the dungeon, and then does Mind Card to Mokuba right then and there:
…but without playing a game with him first.
I, look. The manga establishes that Penalty Games have rules. They’re a punishment for losing a regular game, just like the IRL penalty games in game shows that they’re based off. The early manga showcases Yami Yugi giving a different penalty game every time; in the anime he always gives Mind Crush. Whatever. The point is that, the Millennium Items oversee the regular game, they judge the hearts of the two people playing, and whoever wins the game is considered to have the stronger heart.
(Tangent – This is the whole damn point of all of Yu-Gi-Oh: the meeting of hearts, shown through the medium of games. This is why every protagonist since the dawn of time has believed all his opponents are his nakama: because he can make a legitimate claim that he knows their hearts.)
If Pegasus can just magically hurt someone without playing a game first, why would he ever play a game with anyone in the first place?
Need Kaiba out of power at Kaiba Corp? MIND CARD. Need Yugi Mutou out of the picture? MIND CARD. About to lose a tournament? MIND CARD. So what if he needs the reputation of being the strongest duelist in order to be hired? Just MIND CARD every who stands in his way!
Ok, I mean, I guess you could make the argument that Pegasus and Mokuba played a game off-screen, and Pegasus just held off on enforcing the Penalty Game to mess with Kaiba. Hell, I can imagine he would do that. But if the show has time to show Pegasus watching everyone like a creep but can’t even be assed to explain why he’s done Mind Card to Mokuba, I think the anime writers just didn’t care.
And if you don’t headcanon that Mokuba himself challenged Pegasus to a game of Capsule Monsters for KaibaCorp, and that’s why he got Mind Carded… I don’t think we can be friends.
There’s no real difference between the duels, so I won’t really deal with it (it’s the duel with the Paradox Meikyu brothers). The manga does have a sequence where the Yugi-tachi try to figure out the exit from the duel chamber that is important for two reasons.
The less important reason is just that it shows some of Yami Yugi’s thought process on how he comes up with the coin trick. Maybe that’s only important to me because I’m a die-hard Yami fan, and I prefer him as a smart asshole instead of just an asshole, so I like seeing how he thinks.
The more important reason is this:
a glimpse inside the relationship between the two Bakuras, as well as a very important character establishment moment for both of them. Yami Bakura uses peoples’ feelings to be a manipulative bastard. Regular Bakura is ultimately heroic, but totally gullible.
This of course is dropped from the anime, because at the end of the duel between Yami Bakura and Yami Yugi, the Yugi-tachi apparently just lets Bakura keep the ring. Despite Yami B stating that he’s an evil spirit inhabiting it. Logic.
There are a couple other moments around this duel that hint toward Bakura’s relationship with the Ring, so it’s definitely worth a read.