The Purple and Black Entities are a race of sapient beings which reside in the City of Silver Pocket Dimension.
History
Main Universe
At some point, in the prime universe, a transformed Matoran named Gaardus arrived on the red star. These beings then met him somehow. Gaardus eventually left the star.
After Tren Krom's death, Gaardus took Kopaka and Pohatu back to the Red Star, where they were greeted by three of the beings. Recognizing Gaardus, the beings produced three weapons.
City of Silver
When Takanuva arrived in the pocket dimension, he received information from the Spectral Mask that a village was in trouble. Without hearing the complete message of the Mask, Takanuva immediately rushed off, where he saw crowds of the purple and black entities fighting against a large creature. Deciding that the creature was the source of the commotion and what he had to combat, Takanuva fended off the creature, believing to have saved the entities.
However, the entities laughed at Takanuva instead, and locked Takanuva out of the village. It was later that Takanuva learned the entities were actually trying to chase the last of the creatures out of the village, to whom the village actually belonged. Realizing his mistake, Takanuva consulted with the creature and enacted a plan to lure the entities out of the village. He stood outside of the village and created many large fireworks, and the entities flooded out of their village to watch. While they admired the fireworks, the creature burrowed back into the village and locked the entities out.