When Toothless and Hiccup are taken by Valka, Hiccup states that Toothless is unable to fly without his aid. However, later in the film we see Drago flying on Toothless, but he doesn't touch any of the modifications that Hiccup has added to assist in flying Toothless, so how is Toothless able to fly?
After Hiccup and Toothless's first crash landing after flying solo, Toothless's tail fin is seen to be slightly burnt and beaten from the crash, but in the next seen it is perfectly normal.
During the battle with the alpha, Hiccup takes a strip of cloth to cover Toothless' eyes. Just as he puts in on, there is no tear in the top left side, but a split second later, when the camera zooms in, a tear suddenly appears.
When Drago first puts his foot on Hookfang, it is directly above Hookfang's nostrils and in front of a small horn. In the next shot, it is higher up on Hookfang's head.
After Eret begins tying up Stormfly, the position of ropes on her head change between shots.
Hiccup loses his helmet over the ocean and it floats. Since it appears to be made of iron and leather it should sink immediately.
When Valka and Hiccup bond while flying around with the dragons after getting fish, Valka climbs around on the dragons at the thermal, and the dragons are shown to be next to weightless due to the strong air currents. Yet somehow Valka is able to fall a couple feet to reach Cloudjumper, when only moments ago she needed her staff to hold on to Toothless to avoid floating higher.
After blindfolding Toothless, Hiccup changes the tail fin's position, and Toothless hesitates before also doing so. No change in Toothless's flight pattern is seen in any way, although some change in flight would have had to have occurred from the tail fins being in two different positions.
Astrid asks hiccup if the bewilderbeast will take control of the baby dragons that they're flying on , to which he replies , " they're babies , they don't listen to anyone " , he says something pretty similar to this in king of dragons part 2 of dragons race to the edge when atali and the wing maidens show up with the baby razorwhips on their backs .
After the fight ended between Toothless and the Bewilderbeast when Hiccup and Toothless are back together, and when some of the owners are being reunited with their dragons, the backdrop keeps changing from a view of the ocean, and then the next shot has Berk houses instead, facing away from the ocean, but the subjects/characters in the shot are still in the same part of their quadrant positioning, and continues this way about one or two more times.
Eret shows the brand that was burned into his chest to hiccup , this same brand was used in enemy of my enemy when the dragon flyer uses it on a barrel , yet hiccup doesn't seem to recognize it .
In the first film, Stoick gifts Hiccup a helmet made from Valka's breastplate. However, finally being revealed in this film, her bosom is nowhere near large enough for this to be true.
In the BBC One print, instead of the correct 20th Century Fox logo, the Paramount Pictures logo is shown, even though DreamWorks Animation leaves Paramount for 20th Century Fox as distributor in 2012.
Hiccup covers Toothless' eyes so that the alpha can't control him, suggesting that the control is visual, yet the alpha controls all the other dragons without having to look at them.
During the first two times when Hiccup flies with his flight suit, something appears in front of him, requiring Toothless to save him. However, Hiccup could have just turned around or gone straight down until Toothless could reach him, rather than panic helplessly while flying towards the impending object.