Slayer Codex

The Slayer Codex is the book used to record the souls of Slayer monsters that the player has captured. It is obtained from Faiza after achieving level 99 Slayer. The Codex is updated when a new creature's soul is captured in an ushabti and placed in the Chest of Souls, or when it is added to the player's personal Slayer Dungeon.

Souls added to the Codex award 250 base reputation each. Additionally, every 20 souls added to the Codex add a 1% boost to Slayer experience gained while wearing the Slayer helmet, up to 5% for adding 100 souls. After 50 souls are added, the Codex can be used to teleport to the Sunken Pyramid. New murals in the Sunken Pyramid are uncovered with 10, 30, 50, 70, 90, and 110 souls added.

The first ushabti of a creature that the player turns in gives them full experience, and the following ushabti of that same creature gives the player 25% experience. Turning in all souls at least once will complete the Slayer Codex, which will give a cumulative 1,522,375 Slayer experience.

Completing the Codex and having unlocked the red version of the Slayer Master title from Rush of Blood unlocks the golden title.

There are currently souls to capture. Capturing all is a requirement for the trimmed completionist cape and capturing 110 souls is a requirement for the master quest cape.

Slayer monsters
In order to fill the entire Codex, players will need level 117 Slayer (boostable) and level 115 Dungeoneering (which cannot be boosted). This does not include other requirements such as quests and tasks. Some monsters can only be killed when given to the player as a Slayer task (e.g. Desert Strykewyrms).

For monsters that fall under one category, killing any non-boss monster will be eligible for the ushabti to capture its soul. The only exceptions to this are gemstone dragons, stalker creatures, corrupted creatures, soul devourers, and Lost Grove creatures, who all have their own individual categories for the purpose of the Slayer Codex, and ascension creatures, as the Legiones bosses may be killed for a soul. When the ascension creature soul is captured the tooltip will display "Ascension member", however when one uses the check option on the Ushabti it will state exactly which member's soul is contained within. All monsters that fit in the small room will fit in the large ones as well.

Having soul devourers or corrupted creatures in the player-owned Slayer dungeon, while having toggled auto loot on in the chest in the Sophanem Slayer Dungeon, does not affect the drops in the player-owned Slayer dungeon. The items will instead drop on the ground. Killing them does not grant reputation within Menaphos, the corruption debuff is not received, and feathers of Ma'at are still required to complete the kill.

Trivia

 * TzHaar and volcanic creatures are slayer categories not included in the Slayer Codex, likely due to their souls being trapped in Tokkul.
 * The Acolytes of Seiryu are also not in the Slayer Codex despite being Slayer creatures. This includes Anagami, Arhat, Sakadagami, and Sotapanna.
 * A boosted Slayer level does not count towards the likelihood of getting a soul.
 * Players who had monsters added to the Slayer Codex prior to 26 June 2017 were retroactively awarded 250 reputation for each monster.
 * All grotworm souls are referred to as mature grotworm souls when deposited in the Chest of souls.
 * Baby dragon souls appear as adult dragons in the Sunken Pyramid.
 * Guard dog souls are referred to as wild dog souls.
 * There was a glitch where only 90 rather than 110 souls were required for the master quest cape. It started on 4 September 2017 and was fixed 7 weeks later on 23 October 2017.