Cody Sunn-Childe used the phrase Monster-brother to describe the psychic, external forms that his intense, aggressive emotions took.
To preserve his own tranquility, he allowed these entities to wander freely throughout the Kingdom of Dreams's jungles. However, after Chewbacca and Lando Calrissian incited some of the creatures to acts of aggression, Sunn-Childe had no choice but to reintegrate them back into his own being.
Subsequently, Cody's anger was triggered by Captain Plikk's assault, resulting in the release of the monster-brothers as enormous demons that then proceeded to attack the Imperial fleet.