This is a Chinese mystical action adventure. It's a sequel to Mojin: The Lost Legend, both of which are based on a series of popular books. During the opening exposition we are told that a thousand years in the past Princess Jingjue, who keeps a snake on her shoulder like a parrot on a pirate, created a cruel punishment to subjugate her people. Anyone who tried to oppose her was cursed with an eye-like mark on their shoulder called the Ghost Eye Curse. In the end they would die in terror and to make it worse, the curse was passed from one generation to the next. Anybody with the curse won't live longer than 40 years. The only way to break the curse is to get two things, the Dagon Bone Celestial Tome, and the Mu Chen Orb. When they are combined as one, the curse will be lifted. At the end, during the snake scene, we see a flashback that shows the princess give the Orb to the snake which then swallows it. Then we see the snake crawling through many different seasons over a large timespan until it crawls up a mountain and fades into the ground, becoming a part of the mountain. A thousand years later we see the Orb on a large statue at the tomb of an Emperor that is guarded by that dormant snake.
As you would expect, lots of people have tried and failed to find the Tome and the Orb, but nobody succeeded. The latest to try is Professor Sun. He smokes a pipe, so you know he's smart. Somehow he already has the Tome. Maybe he found it in the first movie, which I haven't seen. He translates inscriptions on the Tome and learns how to find the Orb. Then he and a group of five young men and women travel to Yunan and Hidden Dragon Mountain to find the Tomb of Emperor Xian where the Orb is hidden. Along the way they are shown strange glowing flying insects called flameflies, they climb up to a floating island, and ride rafts on an underground river. Armed with knives, swords, arrows, flamethrowers, a slingshot, the king of all flameflies, and a lot of luck, they fight off off flesh-eating fish, flying bat monsters, giant forest lizards, the giant deathless crab of the Hua Clan, and an army of gigantic scorpions that have huge mouths full of teeth. The final obstacle they need to overcome is the creature that guards the temple that protects the Orb, a giant monster snake, which suddenly appears out of the ground after the hero of the gang named Bayi pulls the Orb off the statue.
The snake is enorous, maybe hundreds of feet long. It's constantly shedding dirt or some substance, and it has the two large fangs on the top of the mouth that movie snakes always have. But it's not a very good temple guard since it doesn't show up until after the Orb is taken. Then all it does is open its mouth and roar then smash its head into the ground when it's trying to catch one of the temple robbers, but it always misses. It never even touches anyone in the group. I was happy to hear that the snake was not accompanied by the usual hissing and rattling sounds we typically hear whenever we see a snake on screen, though it does make exaggerated loud growling and roaring sounds.
I'll spoil the outcome of the fight since it's a unique way to kill a monster snake.
One of the gang named Fatty stole the king flamefly and carried it in its glass jar during the journey. We were told that if the king burns, every other flamefly will come to his side and burn with him since they're more loyal than dogs. When the snake attacks Fatty, the jar falls to the ground and a piece of the glass breaks, letting the scent out. We see flameflies flying and appearing all around the snake. Bayi decides to use the flamefly king to kill the snake but he drops and destroys what's left of the jar, letting the king flamefly escape and fly away. But Professor Sun is able to catch the king in his hand. We have learned that whoever touches the king flamefly will catch fire. The professor slowly catches fire as he runs, calling the snake towards him. Somehow he jumps up and flies into the air into the snake's mouth. All of the flameflies follow the king into the snake's mouth, and the snake catches fire and is destroyed.
The snake is all CGI. It's not perfect, but it's one of the better ones I've seen. It has more sharp detail than we usually see on CGI giant monster snakes, though the bar is set very low.