The Great Devourer

The Great Devourer is a character in the Ninjago storyline. It is a monstrous snake worshipped by the Serpentine as a god, and is believed to exist only to consume all of creation. Only the four Silver Fangblades are capable of unleashing it. It is also responsible for Lord Garmadon's transformation to evil, as it bit him as a child, corrupting him with its evil powers.

Can of Worms
The Great Devourer's existence was hinted at when Cole and Zane entered the Constrictai Tomb. While searching for the inhabitants, the two ninja discovered a crude mural on the wall depicting the Serpentine gathering before an especially massive snake.

Tick Tock
The Great Devourer made its first true appearance in a flashback Sensei Wu had before he set out to find Lord Garmadon's Dimension, when the old man told his students how Lord Garmadon's descent into evil began when he was bitten by a strange green snake in the bushes. Wu explained that the snake - a young Great Devourer - was a legendary beast, said to consume everything in its path, growing ever larger and stronger until it brought eternal night upon the world. He charged the Ninja with finding the four Fangblades before the Serpentine could, as the Fangblades were the keys to the Devourer's revival.

The Rise of The Great Devourer
Despite the ninja's best efforts, Pythor P. Chumsworth managed to collect all of the Fangblades and retreat to The Lost City of Ouroboros, where the Devourer was thought to have been imprisoned. Placing the Fangblades in the teeth of a great statue, Pythor commanded the Devourer to awaken, expecting it to emerge from the statue. To his surprise, the beast was not within the statue, but beneath the Slither Pit arena itself, and it was far larger than Pythor had expected. More frightening still for the Anacondrai General, Sensei Wu revealed that the Great Devourer had no qualms about eating the Serpentine along with the rest of the world, and the monster proved him right when it made Pythor and Sensei Wu its first victims upon release.

The Day of The Great Devourer
The Ninja attempted to escape the Devourer in the Destiny's Bounty, but they only succeeded in making the beast even bigger when it ate their jettisoned ballast and the ship itself. However, the escape gave them time to reach Ed & Edna's Scrap N Junk, where they used a Tornado of Creation to build the Ultra Sonic Raider. Equipping their new vehicle with Zane's recording of the Sacred Flute, they managed to deal some damage to the Devourer, also discovering a small weak spot on the top of its head. However, the Great Devourer destroyed the Ultra Sonic Raider's sonic cannons and withdrew to attack Ninjago City.

The Ninja followed the Great Devourer and managed to prevent it from consuming any innocent civilians, but the monstrous snake proved too powerful for them to defeat. Even the arrival of Nya's Samurai Mech and the Ultra Dragon did little against the Devourer. Eventually, Lord Garmadon arrived and revealed that the only way to slay the Devourer was to use the power of all four Golden Weapons, which only he could do. Despite their misgivings, the Ninja agreed, with Kai also telling Lord Garmadon about the Devourer's weak spot.

While Lord Garmadon left to prepare his attack, the Ninja distracted the Great Devourer, leading it on a mad chase around the city. Eventually, they were able to immobilize the beast by tangling its body in buildings and tricking it into biting its own tail, leaving its weak spot wide open as Lord Garmadon combined the energies of the Golden Weapons with his own dark powers. Declaring his actions as vengeance against the Great Devourer for dragging him down the path of evil, Lord Garmadon leapt from a skyscraper and plunged through the creature's weak spot, causing the Great Devourer to explode spectacularly.

Darkness Shall Rise
Despite its destruction, the Great Devourer's evil influence continued to plague Ninjago - literally, as its defeat flooded the city with venom. The Ninja spent a large amount of time helping the city's cleanup efforts. When Skales was attempting to assert his leadership over the Serpentine, Skalidor suggested unleashing the Great Devourer again, only for Skales to strike the Constrictai General for the bad idea.

Double Trouble
Lord Garmadon called his Serpentine forces together on the Black Bounty for a brainstorming session on how to defeat the Ninja with his new Mega Weapon. Upon hearing that the weapon could only create, not destroy, Spitta suggested recreating the Great Devourer. Lord Garmadon was not amused by the idea, and had the Venomari Soldier thrown overboard as a sign of his displeasure.

The Stone Army
Despite the Great Devourer's death, its venom has been transporting through the sewage pipes of Ninjago City, and some dripped into several pieces of Stone Army merchandise at the Ninjago Museum of History, bringing them to life. Later, some more venom dripped on the Giant Stone Warrior exhibit found by Misako, bringing the ancient soldier to life.

The Day Ninjago Stood Still
More of the Devourer's venom seeped deep underground, activating an entire army of Stone Warriors sealed in a hidden tomb unearthed by the Serpentine - although this also ended with the Serpentine themselves being sealed away once again.

Abilities
The Great Devourer had an insatiable appetite and the ability to consume anything that it came across. Whenever it consumed something, it grew larger and more powerful - the Ninja noted that it would have been truly unstoppable if allowed to consume the bustling metropolis of Ninjago City.

In combat, the Great Devourer normally used its tremendous size and high invulnerability to its advantage, attempting to swallow anything in its path and smashing opponents with its spiked tail. Its venom is capable of bringing inanimate objects to life and can corrupt even the purest individuals into wrathful,homicidal megalomaniacs against their will.

The Great Devourer only displayed two real weaknesses over the course of the show. Like the Serpentine, it appears to be intolerant of the Sacred Flute's music, to the point of physical pain. It also has a small weak spot on top of its head - if it takes a particularly powerful blow to this point, it will be destroyed.

Trivia

 * According to Kai, the four Silver Fangblades were made from the original teeth of the Great Devourer.
 * Though the Great Devourer is considered a ruler to the Serpentine, they immediately hid in fear of it, as they were avoiding the considerable threat of being eaten.
 * Since the Overlord is the true source of evil in Ninjago, it can be implied that the Overlord might be responsible for creating the Great Devourer; if that's true, then the Overlord is indirectly responsible for Lord Garmadon's transformation to evil, as well as the series' events.
 * The Ninja immobilize the Great Devourer by tricking it into biting its own tail. This is another reference to ouroboros - often depicted as a snake eating its own tail - the concept of cyclical events and entities.
 * The Great Devourer has only appeared in one LEGO set, 9450 Epic Dragon Battle. Physically, it bears more resemblance to the young Devourer seen in Sensei Wu's flashback in "Tick Tock", and it is significantly smaller than the Devourer seen in the show - in fact, it appears to be approximately the size of the statue in Ouroboros' Slither Pit.