<Tr> <Th> 20 </Th> <Td> 20 </Td> <Td> "The Siege of the North, Part 2" </Td> <Td> JM Animation </Td> <Td> Dave Filoni </Td> <Td> Aaron Ehasz </Td> <Td> December 2, 2005 (2005 - 12 - 02) </Td> <Td> 120 </Td> <Td> 3.42 </Td> </Tr> <Tr> <Td_colspan="9"> Zuko struggles to find shelter in the freezing temperatures of the North Pole, while Sokka, Katara and Yue search for him and Aang . At the Northern Water Tribe, firebenders and Fire Nation tanks manage to infiltrate the city . Admiral Zhao slays the moon spirit, Tui, and the waterbenders lose their ability to waterbend . In anger, Aang, who along with Zuko was rescued by Sokka, Katara and Yue, goes into the Avatar State and, in joining with the Ocean Spirit La, destroys the entire Fire Nation armada and army, with the exceptions of Iroh and Zuko . Yue, who was imbued with some of the energy of the Moon Spirit when she was a baby, sacrifices her life to revive it, and becomes the Moon Spirit . Zhao is pulled underwater by the Ocean Spirit in retaliation for slaying the Moon Spirit, refusing to accept Zuko's help when he attempts to save him; Zhao is never seen again . At the end of the episode, Ozai assigns Azula a mission: to hunt down her traitor uncle and brother . </Td> </Tr> <P> Nickelodeon started releasing Season One DVDs in North America on January 31, 2006 with a series of single - disc sets containing four episodes per disc . Later the Complete Book 1 Collection was released on September 12, 2006 containing all twenty episodes plus extras on six discs . </P> <P> PAL versions of the single - disc volume sets started being released on February 19, 2007; . As with the original Region 1 NTSC DVDs, each set contains four episodes per disc . The Complete Book One Collection was released on January 26, 2009 containing all twenty episodes on five discs . These Region 2 releases lack the commentary tracks and other DVD extras found on the Region 1 releases . </P>

Avatar the last airbender season one episode four