S4·E13 Ninja Twilight

Jackie, Uncle, Tohru, and Jade discover that they have overlook something in the ancient writings by making the horrible mistake of placing the final oni mask along side the other eight in Section 13. By doing this, they have released Tarakudo and his generals from the masks that bind them. The entire world begins to be engulfed in total darkness as the shadokahn are now free to walk the earth.