Yu-Gi-Oh! GX (2004)

Grave Risk: Part 2 - S1-E28

Continuity mistake: At the end of the battle between Jaden Yuki and Gravekeeper's Chief, just as the explosion settles, in one shot you see the Gravekeeper's Spear card to the left of Gravekeeper's Chief on the duel disk. However in the next shot Gravekeeper's Spear is replaced with Magician of Black Chaos, which Chief neither has in his deck or ever played in the match. (00:13:35)

erazr

Tag Team Trial: Part 2 - S1-E11

Other mistake: Syrus summons to the field Drillroid and has it attack the Gate Guardian in defense mode, but is blocked by Defence Wall because of its effect, and Defense Wall is destroyed. Because of this, Jaden and Syrus lose 500 Life Points. While it does seem logical that their life points would go down because Drillroid has 1600 attack points and Defense Wall has 2100 defense points, they should not lose life points in the first place. This is mainly due to the fact that Drillroid's effect causes a defense position monster to be destroyed instantly, without losing life points. If Drillroid was capable of destroying Defence Wall, then their life points should have remained at 1700. (00:08:00)

Casual Person

Graduation Match: Part 1 - S1-E51

Audio problem: After Jaden and Zane shake hands and the duel starts, there is a wide shot of the arena where the students are heard cheering for them. But the students all appear to be sitting completely still and motionless, and their mouths don't move in any way. (00:06:35)

Casual Person

Tag Team Trial: Part 1 - S1-E10

Syrus Truesdale: First, I'm going to summon Gyroid in attack mode.
Para: You must be joking. I am surprised that thing even has an attack mode.

Tag Team Trial: Part 1 - S1-E10

Chancellor Shepherd: Jaden, I'll leave it up to you, son.
Jaden Yuki: Ah, these guys couldn't even beat male pattern baldness so there's no way they're going to be able to beat us.