This mod allows the player to select in gameplay option menu, which of the stygian difficulty setting they want to experience.

As there are already darkest settings on the same option page, this mods creates described below settings for stygian:

Resillent enemies:
Gives encountered enemies stygian HP amount once they spawn.

Cruel enemies:
Enemies cast their skills by their stygian difficulty properties, before they telegraph them.

Common Stress:
Heroes have greater chance to receive stress on stygian percentage chance.

Expensive Hamlet:
Upgrades costs are as expenisve as on stygian.

Frail Torches:
Light is fading by exploring new areas at the rate of 7.

Just those 5 above, since it's the player's decision if he wants to delete his save file upon reaching 86 weeks and if he wants some dakrest settings to be disabled or not.

If the player selects stygian as a default difficulty, it is impossible to turn off above stygian settings from gameplay menu, unless Heart of Darkness is killed. This means this mod allows the player to lower stygian mode's strictness, after the final boss is passed.

Final Note: Bloodmoon mode does exact same thing about this mod with known already increasement of weeks to 100 and maximum deaths of 16.

I already drew in the comment section of this steam group details about this mod.

Basically the player has one more path to explore in the old road to finish.

Footnote:
On stygian mode the fifth box of the corridor features thorns, that needs a shovel to be destroyed. If the player didn't have dropped a shovel before he will have to damage his heroes in order to progress.