From Creatures Wikia
The Killer Grendels are an evil breed by Grendel Man. They were made to combat the Hunter Norns. They have hunting genes that allow them to track down norns and ettins with great skill. They also start killing from the day they are born, and don't stop unless they run out of prey or die. They are amphibious. They are somewhat like the Anger Grendels Version 3, and like anger grendels, anger makes them nearly impossible to kill. They also use the same sprites as the V3 angers, but are differently colored.
They can be found at KnyteTrypper's C3/DS Nexus.