there was a rune that says "hex" and I have no idea what it does. could someone tell me please?

From the Worn Notebook

Applies the Hex effect up to level 5. Hex increases any damage taken by a small amount while the user is afflicted by poison, wither, or fire. Additionally, Hex cuts the rate of Mana Regeneration and healing in half.

I didn't add Hex, that's something in base Ars Nouveau that was added, should be in the Worn Notebook