To gain this Achievement you can do this on the first Behemoth. If you kill the Behemoth without breaking all its parts, you'll be able to do it again.
The first Behemoth has 8 breakable parts: 2x legs, 2x arms, 1 head, each side of he's ribs and he's Tail. You can tell what parts are breakable (the Behemoth has baby blue marks) and when a Behemoths part has broken it'll turn purple.
Yellow Damage indicates you're doing damage to a part of the behemoths thats breakable.