We've gotten four abilities from the codex pertaining to melee, ranged, magic and constitution.
Enter a fifth ability, this one for Necomancy:
Miasma Gate
Threshold ability (Necromancy's first)
Effects
Opens a portal that takes up a space of 5x5 tiles over the target. All enemies that find themselves on the area receive 15–30% ability damage every 1.2 seconds for 12 seconds.
(this is basically Magma Tempest for Necromancy, but as a threshold rather than a basic. adjustments can be made for this effect because I kind of don't want to overshadow Magma Tempest with this)
How to acquire
The ability cannot be read directly from the codex. Instead, the player has to first be able to identify that the codex contains a hidden passage. This would require level 80 in Necromancy.
Next, the player has to perform a Greater Ensoulment ritual, selecting the codex as its focus.
Once ensouled, the player, with 20 greater ghostly ink and 5 ectoplasm, can write in the codex,, revealing the hidden ability and allowing the player to unlock it.