Board Thread:Questions and Answers/@comment-112.204.202.95-20130103175927/@comment-5955686-20130105210642

I'm not sure since I'm not G-Rank yet, but if it follows the same formula as the Pale Bone(?) you have to break both the Head AND the Back for it to appear on the rewards.

Even then, it's a rare item, so I recommend getting Luck Booster and Tranquilizing Guru, and then capture it.

Hope this helped.