The codex section contains various challenges where the player has to sacrifice, also known as register, items. When the player completes a codex, it will increase the attributes of the character, or sometimes all characters of the player on the same server. It is unlocked when reaching level 10.
There are four types of codices.
Character codices increase the attributes of the character that completes it.
Reputation codices also increase the attributes of the character only. To complete them, special items crafted from demon charms are necessary.
Server codices will increase attributes from all characters a player has on the server where the codex has been fulfilled.
Time Limited codices are often related to current events (like the global release). Contrary to the other codex types, time limited codices are not permanent. The bonuses will only apply for the duration of the time limited codex.