Also referred to as Elder Dragon, they are dragons that dwells in the Dynamis. Their origins are unknown. Because they have excessively received the Dingir's influence, despite having reached Depth IV—which by all rights is not surprising if their soul incinerates anytime, they are unique existences that has not yet perished.
Bahamut, Leviathan, Hraesvelg, Fafnir, and Nidhogg are the five confirmed Wicked Dragons.
"07 December 2017" addition
All of them were destroyed with the effort of 5 Z/X user chosen by the Dragon Miko of each worlds.
All Wicked Dragons are Cost 8 Z/X with 12000 Power and Level ability that triggered when they appear in Square. All of them were released during the course of Heroic Saga X events.