With our current knowledge of biology and creature design (which is by NO MEANS perfect or even near perfect), a creature of such huge size is not possible. 776 feet long flying creature? Extremely unlikely.
The largest creatures of all times is the blue whale, topping at 177 tons. And it prefers living in deep waters. A blue whale is only ~100 feet long (30 meters). At 776 feet, your creature is 250 meters long! Let us assume it has a lighter body type (not deep as blue whale's). My estimates vary between 300 to 600 tons (300 for a hollow-boned, snake-like creature and 600 for a sturdy-skeleton, heavy set creature). Moving a creature of this much size isn't easy.
Flight (are you joe-king)?
So far, the largest flying creatures of all times are quetzalcoatlus and hatzegopteryx which were ... sorry to disappoint you ... only 40 feet (13 meters) at wingspan. The important thing here is that scientists agree that this is the upper limit on the size of a flying vertebrate. If a creature larger than this tries to fly, the weight of the wings would be so great that it wouldn't even be able to lift its wings at all! If you add more muscles, the wing's weight would further increase and you would require more muscles to lift it which would increase its weight even more and then ...
So no. With current creature design models (which, I repeat, are by no means perfect!) you cannot get any flying creature larger than 13 meters. Forget 250 meters at all!
Feeding Concerns And Reproduction
Living things need to eat. And ... it happens that living things reproduce to form babies just like themselves. Which means that your giant, kraken sized creature will require food which is between 300kg (for reptilian, cold blooded lifestyle) and 1000kg (for mammalian, warm blooded lifestyle).
Now consider that all creatures tend to make babies and proliferate their species. Two such dragons living together in an area would quickly deplete the area of wildlife (they will eat and kill a lot of it and the others would migrate out of fright and habitat destruction due to excessive forest fires). And then their babies would hatch out of those human-sized eggs and populate other parts of the region and ...
If you do get a creature of your size, it would be impossible to move it. The largest land creature to walk the earth was probably amphicoelias and at 190 feet, it weighed around 125 tons. Amphicoelias was a slow, lumbering creature. You can guess yourself what would 300 tons (minimum estimate) would be like.
Your creature would require enormous lungs. Oxygen is absorbed, based on surface area and that means ... trouble for your dragon. If you increase the volume of an object (linearly) 100 times, the surface area would only increase by 10 times. That means ... well, your creature would quickly suffocate to death soon after getting to a large enough size. The only way it can breathe successfully is if the oxygen content in the air increases to at least 50% as opposed to 21% of today. During the Carboniferous Period (359 to 299 mya) the oxygen content of the air was at nearly 35% and there used to be huge insects. Later when the oxygen content fell to 21%, those huge insects disappeared completely forever simply because there was not enough oxygen in the air to let them breathe. The same is going to happen to your dragon.
So, all in all, no. A creature of such size has never evolved in the natural history of life on earth (as far as we know yet) and there is practically zero change that it will evolve in the future too, if the ecological conditions remain the same. Even if you build such a creature with genetic engineering, it would be impossible for it to move (once it reaches maturity) or even breathe fast enough to stay alive!