Due to the experimentation of a certain Neogi, a number of the good people of Hengal (specifically: those who were affiliated with the local Warbond cell) suffered one of two mutations when exposed to stress. Either they "hulked out", rapidly gaining muscle mass, or they "gumbied out", stretching suddenly. The cause of this mutation was a ritual which involved implanting crystals into the heads of the victims, which then errupted from their foreheads when they mutated.
These mutations also impeded their mental faculties, making them mindlessly aggressive. Once the mutations had occured, they were irreversible, as destroying the crystals killed the mutants However, somebody who has undergone the ritual can have the crystal removed relatively safely if they have not yet mutated. As safe as brain surgery in a world without antiseptics can ever be, anyway.