LEGO Ninjago: Masters of Spinjitzu

In the episode Kai and Nya are taken back to the Fire Temple by the fire dragon, named Flame. At first thinking he was homesick, the dragon shows another entrance to the Underworld, hidden within the temple's catacombs. The Skeletons try to get out and Kai attacks, but is quickly overwhelmed, despite his insistence that he can handle it. Nya helps him out, beating the Skeletons back despire her brother's protests, and Flame seals the entrance. The three fly off and the Skeletons smart in their defeat, now firmly trapped in the Underworld, for now.