Can be found in Shadow's Edge on 2F in the time of past. To get to the room: Grapple to the first post in the tube-shaped room you climb up on the eastern side, jump off to the opposite side to get to a pathway that leads you to the chest with the Dungeon Map. On the right side in the pathway you can use Death Grip to climb up the wall and reach 2F.
|“|| Forged in a blast furnace by the demon lord Belial, the Demonflame Renders flare with hellish heat and flame that causes enemies to explode into flames with every strike. Originally meant to serve as a gift to secure favors from Lilith, the Renders were stolen by one of Belial's many rivals... or so he claimed. Whatever the truth, the scythes disappeared for an age, lost or secreted away. The merchant Ostegoth claims that the scythes are loose, seeking out a new and more worthy owner - perhaps these weapons are possessed of a similar hubris to the Demon Lord who created them.|
— In-Game Description, Darksiders II