Cassie, Lorca, and Wheezie are strangely unaffected by the Sleepytime Fog in "A New Friend."
After Ord lays the tree half across the river for he and Lorca to cross on, the other half that was lying there disappears. (The tree halves were also not there when the gang got to the river in the first place.)
Interestingly, Lorca requires no explanation as to why and how these two humans are in Dragon Land.
Max and Ord decided to make another whadayoucallit just like the first one. However, on the second whadayoucallit, the structures were painted purple, while on the original they were painted red.
When Max, Emmy, and the dragons are in the School in the Sky for art project day in "Breaking Up Is Hard To Do," the ceiling of the school is just a layer of grass on top of rafters, but when they go back to the school for Ord and Max to make a new project, the ceiling looks like a flat, white layer of drywall with a brown, dashed line painted on it.
During art project day at The School in the Sky in "Breaking Up Is Hard To Do," Wheezie accidentally smudges paint on Zak's art piece. He appears to wipe it off, but after school is out and Cassie is talking to Max and Ord about sharing their project, the smudge is still on Zak's project. However, after that scene, the smudge disappears and is gone for the rest of the episode.
When Giant Max is tapping his pockets for a coin to wish himself back to normal size, Zak & Wheezie are reversed; Zak is on the left and Wheezie is on the right.
Emmy's souvenir from the theme park in "One Big Wish" changed many times; from the number of cars on it (3, 3 1/2, or 4), what color the cars were (orange or purple), and whether it had one side (end of episode) or two sides (beginning of episode.)
In "Big Funky Cloud," after Ord's friends failed to cheer him up again with a parade, Zak says, "Oh, this never ever, ever going to work!"
You will hear Ord answer, "Zak's right. I will be sad forever and ever and ever!"
but it is different when you use closed captioning. Instead of Ord saying "Zak's right," the text says "That's right."
In the beginning of "Copy Cat", Emmy puts a sixth stick on the roof of her juice pop stick house, but after the camera pans over to Max and back to Emmy, the last stick that she placed mysteriously disappears.
In "Big Funky Cloud," Ord had a big funky cloud on the top of his head and it follows him where ever he goes, but in "The Forest of Darkness" and many other episodes, Ord turns invisible when he feels sad or scared.
Priscilla, the "Ugly Dragling" from Season One, returns as the head of the Dragon Land Lost and Not Yet Found in "Finders Keepers".
When Max and Emmy get to Dragon Land in "Finders Keepers", Ord picks them up for the usual "hello hug", and seems to fly very high into the air according to the fast-scrolling clouds in the background. However, when Emmy tells Ord to let go, he's somehow only about 10 feet in the air.
When Max and Emmy return home in "Finders Keepers," they are still mouthing the words to the rhyme to return home, even though the rhyme should have been completed in Dragon Land for them to return home.
In "Remember the Pillow Fort," pillows come in different colors and from trees, but in "A Liking to Biking" Ord pulls a white pillow from a "pillow cloud."
After Ord was pulled out of the hole in "Very Berry," and is about to hug Zak and Wheezie, Zak's leg is purple instead of green.
There were couple of stock dragons competing in the events in the Dragon Land Fair in "Cassie Catches Up," but in the last event, bobbing for apples, they're never shown them taking a turn.
Emmy asks Ord what "Fly Time" is. She should know though, based on having been told in "A Cool School."
Near the end of "Ord Sees the Light," Ord's dragon badge glows. It's the entire thing though, not just the round, crystal section in the center. This is the only known episode in which that happens, making it a definite mistake.
When Max and Emmy arrive in Dragon Land in "Ord Sees the Light," Emmy is still holding the dragon scale. This is a mistake; it is supposed to go back into the box in their playroom to be used when they go again. Thanks to PBSKidVid for spotting this mistake.