Blue-purple Clusters.
Among Clusters, they were considered to house beasts that were more often than not harder to deal with for your average mercenary, even if they bunched up to form large teams of highly relevant powers.
It just so happened that when Clusters crossed into the purple threshold, the worlds within them became extraordinarily large and complex, some even spotting absurd features like suns and incredibly abstract concepts like powerful religious beliefs that were very real as well as unusual Rules.
As for the creatures that were housed within and the Cluster Generals whose mana kept the entire Cluster stable...
Well, that went without saying. They were powerful.
"Why is it so dark?" Red Rage asked while looking to and fro.
The gleam from his body could not overtake the darkness that he and his master had spawned into. This was the second time his light had failed to shine over the surroundings.
Quite disappointing.