Mega Weapon

The Mega Weapon was a weapon created when Lord Garmadon brought the Golden Weapons to the Golden Peaks.Garmadon unlocks the full potetial of the golden weapons.

Darkness Shall Rise
Lord Garmadon used the Golden Weapons' power to recreate the Destiny's Bounty as the Black Bounty. He used the ship to reach the Golden Peaks, where he united the Golden Weapons into the Mega Weapon.

Pirates Vs. Ninja
As the Black Bounty left the Golden Peaks, the Serpentine asked Lord Garmadon about the capabilities of the Mega Weapon. Garmadon did not know, but the discussion was halted when the Ultra Dragon flew by. As the Black Bounty flew in pursuit, Lord Garmadon tried to use the Mega Weapon to harm the Ultra Dragon. To his dismay, nothing happened, but Garmadon covered his impotence by claiming that the Serpentine's poor piloting skills ruined his shot.

Before the Serpentine could question him further, Garmadon retreated to the captain's quarters and angrily wondered why his Mega Weapon failed to activate. In a fit of rage, he struck a nearby desk, opening a secret compartment containing Captain Soto's log. Upon reading it, Lord Garmadon realized that the Pirates were more competent than the Serpentine and wished to have a crew like them. Suddenly, the weapon seemed to react, glowing brightly and draining Lord Garmadon's energy.

As he tried to catch his breath, Lord Garmadon heard unfamiliar voices above the room. Up on deck, the Serpentine were arguing with none other than Captain Soto's crew. While they were arguing over the ownership of the Black Bounty, Lord Garmadon realized what had happened: the Mega Weapon could only create, not destroy, and the strain of its use meant that he could only use it once a day.

Double Trouble
Now knowing the limits of his Mega Weapon, Lord Garmadon consulted his minions on ideas for defeating the Ninja. After several poor suggestions (including recreating the Great Devourer, creating another group of pirates, and making a really big ham sandwich), he used the Mega Weapon to create the Bizarro Ninja to match the power of the real Ninja.

Ninjaball Run
When the Black Bounty began pursuing the Ninja in the Ninjaball Run, a Venomari Scout asked Lord Garmadon why he didn't use the Mega Weapon against their opponents to ensure his victory. Garmadon reminded the Serpentine that he could only use the weapon once a day, and thus intended to avoid using it unless he had no other choice. Instead, Lord Garmadon attempted to stop the Ninja with his other assets, firing at them with the ship's cannon and sending the Serpentine to attack.

However, all of Garmadon's attacks failed, and he eventually found himself neck and neck with the Ninja's Ultra Sonic Raider in the final leg of the race. Desperate to stop them from winning the money they'd need to save Dareth's dojo, the four-armed villain wished for an obstacle that the Ninja could not overcome, and the Mega Weapon created a massive chasm in the Ninja's path. The power drain left Garmadon unable to defend himself when the police caught up with him after the race, but Skales picked him up in the Serpentine Bus.

Child's Play
At the Ninjago Museum of History, Lord Garmadon used the Mega Weapon to resurrect a prehistoric creature known as the Grundal to hunt down the Ninja. The Ninja interfered, delaying the Grundal's resurrection, but also transforming themselves into children.

Wrong Place, Wrong Time
When the Ninja confronted Garmadon in The Lost City of Ouroboros, he attempted to use the Mega Weapon against them, only for the tip to be frozen by Lloyd. Lord Garmadon was forced to flee while his minions fended off the Ninja - infuriated at their continued persistence, he used the Mega Weapon to travel back in time to prevent the Ninja from ever forming and training Lloyd.

The Mega Weapon was nowhere to be seen when Garmadon was masquerading as a Skulkin, but it was back in his hands when he infiltrated his own fortress to speak with his past self. As part of their plan, Past Garmadon sent his future self to attack Past Kai in the Fire Temple, instead of using Shadows. Garmadon waited patiently for Past Kai to save his sister and retrieve the Sword of Fire, and then confronted his past nemesis with the Mega Weapon in hand.

Lord Garmadon continued to wield the Mega Weapon after the present Ninja intervened on Past Kai's behalf, gaining the upper hand despite being outnumbered and unable to use his weapon's creation powers. Unfortunately, Jay had the idea of using the Golden Weapons of the past to match the Mega Weapon, and the Ninja used their elemental powers to overload Garmadon's weapon. Pulling itself from the four-armed villain's hands, the Mega Weapon fused with the Golden Weapons of the past before flying out of the temple and exploding in the skies far above, crashing-landing into the comet Arcturus.

After the Mega Weapon's destruction in the past, the time stream returned to its previous form, and events proceeded as the Ninja remembered. However, in the process, the Mega Weapon was erased from the memories of everyone, save for those present during its destruction.

Codename: Arcturus
During the Nindroid War, Pythor revealed that the Overlord planned to become the Golden Master by retrieving the remains of the Mega Weapon and fusing with it.

Trivia

 * The Mega Weapon is exclusive to the cartoon series.
 * Lord Garmadon demonstrates the ability to use the power of Creation with the Golden Weapons, even before he creates the Mega Weapon. However, he only uses it to repair and transform the Destiny's Bounty, so it may be that the separate weapons are only capable of transforming existing objects, instead of creating things on a large scale.
 * The head of the Mega Weapon incorporates details of all four of its component elements; Fire and Lightning on the sides and Earth and Ice in the middle.
 * Although the Mega Weapon is said to drain Garmadon's energy when used (hence the once-a-day limit), its draining effects appear to lessen with time - by the time Garmadon uses it to create a time portal in "Wrong Place, Wrong Time," he barely seemed affected by the drain. It is possible that Garmadon has become more skilled with the Mega Weapon, thereby reducing the amount of power that he expends with each use.
 * In "Pirates Vs. Ninja," Garmadon had determined that the Mega Weapon could "only create and not destroy," but later in the episode it disintegrated a pirate that had attempted to take it. However, Garmadon did say that only he can hold the Mega Weapon, implying that anyone else who tried to hold it would suffer the same fate as the pirate.
 * One of Jay's weapons in 70740 Airjitzu Jay Flyer is close to how the Mega Weapon would look in set form.