These are an Old Peoples, the original occupants of Daletal. They have been displaced by the Humans into the back corners of The Six Lands and the Badlands. For generations they waited for a sign so they could take their revenge against the Humans. The Great One came and led them. They swarmed across The Six Lands and ruled! Then The Fall occured. Their numbers have been greatly reduced since the time of their vengence, the Time of Merideth. They have returned to their back corners of The Six Lands. They wait for the Return of the Great One.
The Sleeping King is a near mythic figure that has a presence in real history. Originally called the Lost King, he came from a Land to the East where he had been a King. He left his Land because he felt he had failed his people ( the details are vague upon this point). He arrived here to discover a land under the boot of Merideth the Great. He vowed that, “All people shall be free to live as they need to live. No one should live as a slave to a man or fear!” Thus he began to lead. From a small band came The Six Armies Who Were One. Upon the final assault on Merideth, he brought freedom to The Six Lands. Then left, vowing to return if needed.
This powerful and ruthless legendary leader amassed an army of Beastmen and mercenaries conquering most of The Six Lands. His rule was ruthless, treating the people of the lands as slaves. He took the resources he needed for his campaigns without regard for the “sheep” left behind. He oppressed the people for nearly two decades before being overthrown by the Six Armies who march as One and the Sleeping King.
Magic should have side effects, both expected and unexpected - fortuitous and deplorable. Expected side effects add anticipation, while unexpected ones increase the drama of the scene. The result can be comedic or dire, it dpends on which circumstances work best for your game.