Currently, the Abyssal Forge DLC is not appearing under the Season Pass in the DLC menu.
We are aware of the issue and are working to resolve it as soon as possible.
In the mean time, you can download the Abyssal Forge content for free by Searching for it by name in the PSN Store. You must have the Season Pass installed to use this work around.
Enter the PSN Store and select the Search feature at the top of the screen. Enter the letters ABY in the search field. Listed under Darksiders II, select the Abyssal Forge. The price in the bottom left should show as Free.
Download the Abyssal Forge and once installation is complete, check in game under the DLC>Choose Campaign menu.
THQ Customer Service