In the season four finale, "Twilight's Kingdom" Discord is tasked by Celestia with finding and capturing Lord Tirek. However, Tirek tricks him into betraying his friends, giving him a necklace as a token of gratitude and loyalty. After he captures the non-princess ponies for Tirek, he double-crosses Discord by stealing his powers and admits that the necklace has no meaning to him, for it was given to him by his traitorous brother, Scorpan. After a fight between Twilight and Tirek that results in a draw, Tirek trades all of Twilight's magic for her friends and Discord. Discord admits that he now understands the true meaning of friendship and gives Twilight the necklace. The necklace turns out to be the sixth and final key needed to access the chest at the Tree of Harmony. The Mane 6 take it as Tirek starts going on a mindless rampage and they use the newly unlocked Rainbow Power to transport Tirek back to his imprisonment and save Equestria.
