Forest of White Dreams is the ideal location that the Sin of Envy Diane, of the Seven Deadly Sins chose as a hideout to escape from Holy Knights. She had ordered the residents of the forest, Prankster Imps to guard the forest from Indruders, otherwise she would go on a rampage.
Forest of White Dream Arc
Meliodas, Elizebath and Hawk venture into the forest to find Diane. Soon, they are encountered by Prankster Imps who take the guise of Elizebath. Meliodas defeats them and they run back to Diane who is sleeping. She wakes up with a startle and meets with Meliodas and Elizebath.
They weren't even properly acquainted yet when Gilthunder drops from the sky and attacks them. Meliodas and Diane fights the two of them but Meliodas is struck down. He actually got hit on purpose to learn of the location of the rest of the sins. Having learnt of Ban's and King's whereabouts, Diane quickly expelled Gilthunder from their location using her brute strength.
Meliodas however was gravely injured and they started their journey with Diane to the town of Dalmary, close to Baste Dungeon where Ban was held captive.