The Abyssal Forge is the second DLC for Darksiders II.
Believing Death to be a assassin sent by the Makers the two do battle, however the Maker is able to buy his life at the last moment with the promise of answers for his would be slayer. He explains that eons ago he was imprisoned in the void inside the tree and that is where they are.
However something else was imprisoned with him, The Abyssal Forge his finest creation. A sentient forge that draws its strength from the Abyss itself, using said power it has forge an army of constructs also powered by the Abyss over the eons whom in turn can build more Abyssal Forges on other worlds should it escape it's long imprisonment.
Realizing that the lock on their prison has been broken by Corruption the Smith begs Death to help him put an end to his finest creation, lest it threaten creation. In order to reach it safely Death collects a large amount of Chaos Ore for the Smith and using it he makes for him the Mad Smith's Device that allows him to safely cross the toxic waters surrounding the Abyssal Forge's lair.
Making his way to the forge Death meets the Mad construct which confirms the Mad Smith's fears that it plans to rule creation with its progeny, noting that Death is not a Maker but something both demonic and angelic at the same time it demands to know his purpose, to which he states that he's Death. Destroying the construct and returning to the Smith Death informs him that he intends to leave him in the forge with his broken mind.
That said, Death also warns the Smith not to make him regret his mercy.