After Toothless sneezes the background shows two viking statues when there is supposed to be only one.
Fishlegs does not have the Book Of Dragons when he talks about the Scauldron, because the Book Of Dragons does not have stitches on the cover and there is supposed to be a dragon on the cover.
At the part in Dragon Flower when Hiccup and his friends are waiting for the venom out of Mildew's butt, half of Hiccup's face is pinkish red.