Factual error: When the Titanic sinks all six dwarves and Kevin end up in the sea clutching a lifebelt. The water in which the Titanic sank was freezing - that is how most of the casualties died, by freezing, not drowning. In water like that you'd be lucky to stay conscious for more than a few minutes. Despite this none of them show the slightest effect of the cold. Maybe the dwarves have some 'magical' ability to withstand lethal cold, but Kevin doesn't even react to being plunged into freezing cold water. He'd be screaming in pain, but he doesn't even show the slightest sign of discomfort.
Factual error: When the roast ox is cut in half by the swordsman, fruits spill out which were totally unknown to the ancient Greeks - most notably pineapples, mangoes and papayas. None of these fruits were available to Europeans for another 3,500 years when they were discovered in South America and the South Pacific. (And Greek explorers did NOT discover them independently, nor did they trade with anyone who did.). (00:54:45)
Revealing mistake: When Wally is firing the laser at random from the small spaceship, we see Fidget running down some stone stairs, and there are violent laser impacts directly behind him that could only have hit where they did if they had passed right though his body. (01:41:55)
Visible crew/equipment: When Kevin remarks how they must have run into an invisible barrier, the reflection of something can be seen in the barrier. Might be a camera or some other kind of equipment. (01:17:00)
Continuity mistake: When the dwarves find the invisible barrier, Wally takes the map from Randall and calls him crazy. Randall then picks up a skull and throws it, shattering the invisible barrier. At this point Randall takes the map back from Wally, then the camera angle changes and we see Randall taking the map off Wally again. (01:18:05)
Revealing mistake: Right after the party splits in the fortress of darkness and Kevin and his piggy friend are chased by the big horned creatures, one of them fires a ball of flame out of its eye. In the next shot when they run trough the pillars of stone, you can see wires on the ceiling, the burning ball is draged with through the set (in the white smoke). This is even better visible some seconds later when the fireball flies trough the door. (01:30:15)
Audio problem: When Kevin and his crew of thieving little people land in the Middle Ages, Randall informs Kevin that they made all of what's surrounding them, trees, shrubs, bushes etc. Kevin's reply is "Phew, that's not bad" He says this without opening his mouth. This was looped into the film later on.
Continuity mistake: Near the end of the film, there's a scene where the bandits are trapped in a cage hanging from a huge rope. One of the bandits crawls up on top, and severs multiple strands about 4' in length from the rope, leaving the cage hanging from a tiny strand. A bit later, when the cage is being swung back and forth, the missing section of rope has shortened considerably. (01:24:55 - 01:26:10)
Visible crew/equipment: During the scene where Kevin and the Dwarves are pushing his bedroom wall through. When the wall finally reaches the end and falls into space, you can clearly see the Sticky tape protruding from the top of the corridor that was holding the wall there in the first place. (00:11:00)
Continuity mistake: When Wally has jumped off the bottom of the cage and caught the rope, the rope holding the bandits' original cage snaps. This original cage (which has Wally's rope firmly tied to it) falls into the abyss. When the other bandits pull Wally up, there is no sign of the cage, which should have also shown up. Also, Wally is hanging on at the end of the rope, but he was in the middle of it before the cage's rope snaps. (01:28:10)
Revealing mistake: When Kevin walks towards the ashes of his parents after the toaster oven explosion, smoke can be seen going back towards the ashes, revealing that it is reversed footage.
Continuity mistake: In the "hanging cages" scene, when the rope holding the first cage finally breaks and the cage drops, the only thing holding the other end is one of the characters, who was shown earlier with the rope around his chest and holding on by his fingers. He should have been pulled into the abyss when all the slack was gone.