Forge: 14.23.4.2708
Hardcore Darkness: 2.0
PlayersChoice: 1.2-4

playerschoice.json: https://gist.github.com/TeetoKaziim/6d6efa26cc9a9dc4229e57a040c9dec3

Crash Report: https://gist.github.com/TeetoKaziim/041ea0ed41ae428855315561e18b7b45

How it happens:

Using Player's Choice, define Hardcore darkness as an optional mod in config\playerschoice.json.
If you select to have Hardcore Darkness disabled. After the restart, and when you load it again, it will get to the main menu just fine. But, when you open a world, you get the crash in the gist at the top of the issue.

Thanks for having a look. This is a crosspost from their issue tracker too, just in case collaboration is desirable: lumien231/Hardcore-Darkness#36