Garmatron

Garmatron is the ultimate weapon created by the Overlord and his Stone Army. It is, apparently, a large tank with an over-sized cannon as it's primary weapon.

History
In the beginning of Lord Garmadon and the Overlord's associating, the Overlord promised Lord Garmadon of an undefeatable weapon of colossal power. It was stated that when the Celestial Clock were to finally hit the skull symbol, the ultimate weapon would be complete. In Return of the Overlord, Garmatron is finally finished being constructed, and Lord Garmadon is content to operate it. After a few small attacks on Ninjago, the balance is finally altered to be asymmetrical, and the Overlord reveals that he had been plotting against Lord Garmadon since the beginning. After confessing his undertaking, the Overlord unleashes a powerful thunder bolt that struck Lord Garmadon, changing his body into a bizarre, reptilian-looking creature. After having a few conflicts with the ninja, the Overlord soon loses his patience and decides to launch an attack on Ninjago City, opening a portal and leaving with the Stone Army, along with an infected Nya.