Jack has a small candle which he lights, he then pulls the other half over it. This then creates a flashlight effect. Wouldn't the candle burn through the material? And if it is fire-proof, wouldn't it just put out the fire? Besides, it wouldn't focus the light into a beam anyway, would it?
When the thief is going over the security laser beams, wouldn't the tails of his coat hang down and trip the alarm?
What is a janitor's closet doing in one of Aku's high-security vaults? Exactly who is the janitor?
The diamond pattern on the sword's handle is not seen for most of the episode.
When Jack's father is riding the horse, you see the moon is a cresent with a star within its shape. The star which the cresent surrounds shouldn't be there unless the star was in front of the moon (which is impossible) or the moon is actually a cresent (in which case, it wouldn't be able to orbit the planet).
Trivia: Aku's first act of evil when he comes to Earth: annihilating the dinosaurs.
When Aku comes to Earth it is the time of the dinosaurs, but when Earth is shown the landscape is not Pangea.
When the monk that gives Jack's father the elixir is seen from a faraway view, the container of the poison is like a cup. When the view zooms in, it looks like a perfume bottle. Then when Jack's father puts it in his belt, it's a cup again.
Odin wields a trident, but in Norse mythology, Odin wielded a spear called Gungnir, which never misses its target.
In medium shots of the village that becomes Jack's civilization, a river can be seen running though the village, but it's not there in long shots.
After Jack leaves the two Shoalin warriors to fight the statues and goes after the portal why don't some of the dumb statues follow him.
How could those rock statues be able to stay on the wooden bridge without being too heavy to fall through?
Trivia: The stuffed doll looks a lot like Jack's "friend" from "Jack and the Creature."
When the Hermit stands on the glass dome just after dawn, his shadow lengthens as the sun rises.
Hermit/Aku's reflection on the water reveals his true form. But when Aku drank from the oasis as the warrior woman (in the episode of the same name), his image was unchanged.
During the fight between Jack and the time portal guardian, the collar on the time portal guardian's suit keeps disappearing and reappearing.
Trivia: This is the first episode where Young Jack speaks.
Trivia: Apparently, restraining orders still exist in this futuristic world.
As they were seated on top of the train, Jack's hat and Josephine's parasol should have created so much drag force from the speed of train that the items should have flown away.
When Jack punches the DJ in the face the DJ's gold tooth is white. In later scenes the same tooth is missing.