The result of arcane fallout found in the Imperial swamplands, they are fearsome predatory killers with a unique ability.
Grendelbeasts are crocodilian in appearance and behavior, complete with jaws that can crush steel. Their bones are significantly stronger than those of humans, and they have a sense of smell better than a dogs. Studying its brain shows it is not fully sapient, but that it is not far off, and is at least as smart as a gorilla. Its claws are not just weapons, but exert enough traction for the creature to sprint up rocky cliffs. Though it is not a true amphibian – it cannot breathe water – it does possess an integral snorkel enabling it to move undetected beneath several feet of water. Its cardiovascular system and musculature give it strength and stamina far beyond that of most creatures, and that is without its primary evolutionary advantage: A super-oxygenated blood supplement.
A grendelbeast can, on demand, release a chemical supercharger into its blood that enables short bursts of speed in excess of a hundred miles per hour. This is the primary trait makes the grendelbeasts so dangerous – and the key to their destruction. The supercharger, when used, generates large amounts of waste-heat that warm up their bodies so rapidly they effectively “cook themselves” and will die after using it if they do not immediately return to the water to cool off.