This is earned by cutting off a creature's head and two arms. This can be pretty tricky, as you'll often kill them before you can remove the third part.
Grab a sharp weapon, like a Knife, Machete or Hatchet. Try to remove each arm first, by swinging directly at each arm. Once both arms are gone, remove the head by swinging down or stabbing at it. If successful, the head will explode, and the body will stumble around for a moment before finally dying.
Refrain from swinging wildly at it, as that will just cause more damage and kill it before you want to. Do not attack the creature after removing it's parts; allow it to die on its own.