Other mistake: In all the shots of ET wearing the white sheet the two eye holes are about a foot apart, so he could see out of the holes properly, but when Michael finds the white sheet ET had been wearing he lifts the material and we see that the two eye holes are only about two inches apart, which makes no sense. (It was Gertie's sheet that had eye holes so close together).
Other mistake: The shape of the crystal shard is all wrong. In a flashback scene a urSkek is seen "shattering" the original, pure crystal by hitting it with a rod on one of the crystal's flat surfaces. For argument's sake we will say that in their universe it would be possible for this to create a spear-shaped hole in the crystal. However, the top of the shard is a rounded surface; it should have a flat, slanted top to match the top of the hole it came out of. Could pieces have broken off the top of the shard to give it the rounded shape? If that were true the final solution would not have worked; only the whole, pure crystal would restore the urSkeks.
Other mistake: When the thresher blows for the second time, Mr. Ages slides down it into a large chamber into a basket. When he falls into it, he is translucent for a second.
Other mistake: The scene where Robin Ignico mentions Annie's new dog Sandy "but there's no bite in him," Lucy Stewart can be seen re-mouthing Robin's line.