Naglfar

Naglfar is a superboss in Final Fantasy XV fought during the Wondrous Weapon sidequest for Randolph in Chapter 15. Completing the quest yields the superb Zwill Crossblades daggers.

The Squirming Bone key item naglfar yields is the only "monster part" obtained from a daemon. Usually only biological monsters drop monster parts, whereas daemons dissolve into miasma upon being defeated. The description to Squirming Bone describes it as "the partial remains of a deathclaw, still wriggling with life."