Season one (10 episodes) of the show features on aging master Sensei Wu as he struggles to train four young Ninja in the ways of an ancient battle art called Spinjitzu to defeat his evil brother Lord Garmadon, ruler[but not king] of the underworld, and stop him from gaining four golden weapons which would make his power limitless. Though many skeleton characters are introduced, only Kruncha and Nuckal appear in season two, making cameos as substitute teachers.
Season two (13 episodes) focuses on Garmadon's young son Lloyd Garmadon, who, lacking proper fathering, has released an ancient evil army of snakes, who hold unique powers. The four Ninja must stop them from uniting to unleash the Great Devourer, an evil with power to consume the land.