This is a mod initially developed for FTB Nocturne but it has since been adapted for other pack devs to use should they desire. This mod makes players gradually increase flux in the chunk they are in. Once the flux goes above 300 it will begin to convert to defiled lands biome (requires the optional defiled lands dependency) and corrupt blocks similar to the old TC taint spread mechanics (although whether it continues to spread depends on your config setting in defiled lands).
To offset this there is an amulet that can prevent this from happening at the cost of the amulet taking damage.
I also recommend potentially using the Animus bloodmagic addon if it fits in your pack for the eldritch will ritual to help combat this (or not!)
Additionally when the flux is high enough in the area the player will get buffs depending on how much flux in in the area. This is completely configurable or can disabled.
You can have beneficial or negative effects applied with scaling flux values.
The amulet doesn't have a crafting recipe by default, I leave that to pack makers to decide what's right for them.
There are lots of config options for setting the corruption rate/threshold as well as the amulet damage values (You can also make it unbreakable)
You can turn off players generating flux, set all the thresholds for different effects etc, whatever you can think of to work with your pack's vision.
Any bugs or issues please direct to the github issue tracker
If you have any suggestions on content to add that fits with the functionality of this mod let me know.