Talk:Horn of the Abyss (Documentation)
They have an expanded list of new features. Im not sure if there is an english version.  The problem is they've stopped updating it at may 2017 so theoretically there could be an old-new fix conflict (if there are any).
Thats what googletranslate says about spell prohibition:
- Expand the effect of the prohibition of spells on the map.
- Northern Lights (the structure of the Grail of Conjugation) does not allow studying forbidden spells.
- Artifacts Water Magic Book, Earth Magic Book, Air Magic Book, Fire Magic Book and Spiritmaster Hat do not add forbidden spells to the hero. If all spells that give any of these artifacts are banned, this artifact is also automatically banned.