LEGO Ninjago is a theme of LEGO products introduced in 2011. The premise seems founded almost entirely on Rule of Cool: A group of ninjas with Elemental Powers are at war with an army of similarly elementally themed undead skeletons. Both fight using the martial art called "Spinjitzu", which involves spinning at high velocity to channel elemental powers. To support their effort, the ninjas tame powerful dragons matching their elements, while the skeletons command high-tech vehicles like tanks and motorcycles. Later on they battle against the Big Bad's son who unleashes five ancient races of snake people who were the original rulers of Ninjago.