"Punch-blade melee weapon. A relic of assassins from a bygone age, its obsidian teeth cut clean to the bone."
— In-game description
The Nightbreaker (referred to as Bone Glass in the game files) is a melee weapon in Call of Duty: Black Ops III that was added in the June 14, 2016 update. It can be obtained only through supply drops. However, it can be picked up by bots that used it. It can be acquired in Revelations by completing 20 rounds in under 32 minutes.
In terms of appearance, it's much like the Brass Knuckles, albeit with pointed ends coming above and below the hand, and looking more like a set of sharp fangs.