On the Request on Queen Hart they were tasked to check out the Dreamstalk, basicly the source of light based dreams and magic within the world.
Officially it's called the Light Dreamstalk, and it goes down about 50 floors and it sits on the bottom of the light side of the dream world.
The team had started to navigate it but soon they ran into a problem.
They ran into a group of magic users that had retaliated against them and they had no choice to retreat.
Later on they retreated to the dreamworld castle and reported what had happened to the Queen.
"So it appears that he has made a team of his own to do his bidding..."
The king of nightmares with his minions of sorts can be seen in a silhouette type shadow as the queen had spoken behind her in a flashback of sorts.