GulusGammamon is the main antagonist of Digimon Ghost Game, he usually live inside Gammamon's body and watch over Hiro and the others.
A ferocious Digimon that evolved when the evil heart hidden within Gammamon was unleashed. It rejects interference from those around it and is only interested in fighting, and once it catches an opponent that comes into sight, it will not stop attacking them until they breathe their last breath. It puts up ferocious battles where it attacks regardless of whether its limbs get broken.
When GulusGammamon reappeared in Episode 66 of Digimon Ghost Game, it's revealed that he was the one behind the corruption of the Digital World, and revealed the corruption to be the Gulus Realm Burst (GRB), which forces the infected Digimon's fighting instincts to take over. GulusGammamon then revealed he left drops of the GRB all over the Digital World as Gammamon traveled with Hokuto Amanokawa before declaring that the time has come and evolving into Regulusmon.
Regulusmon's philosophy is eat or be eaten, and he explains that his goal is to create an army out of the Digimon corrupted by the GRB Factor. During the fight, Hiro syncs with Regulusmon, a ruse allowing Hiro to bring Gammamon back, which resulted in the group and Bloom Lordmon to be brought into Gammamon's internal dimension as both Regulusmon and Canoweissmon are separated into two entities. Enraged, Regulusmon confronts Siriusmon, Amphimon, and Diarbbitmon, wounding Amphimon with Kalyp Bite. Before Siriusmon can use Breaquazar, Regulusmon launches Amphimon at him and follows up with Genierce, shooting a hole through Siriusmon.
