Sentinels of the Devourer

"...The Devourer's largest spheres of influence."

The Sentinels of the Devourer are three post-Moon Lord bosses that can all be summoned with the Rune of Kos. Defeating all three will give the items necessary to craft a Cosmic Worm, which summons The Devourer of Gods.

The item used to summon the Sentinels, the Rune of Kos, can be crafted before defeating Providence, the Profaned Goddess, but it is also dropped upon her death. Despite each boss being summoned using the Rune of Kos, you must be in the correct biome in order to summon a certain Sentinel. These biomes are the Sky for the Storm Weaver, the Underworld for Signus, Envoy of the Devourer, and the Dungeon for the Ceaseless Void.

Trivia

 * The Sentinels' theme is Servants of the Scourge, which was composed by the artist DM DOKURO. The theme splits to 3 types for each Sentinel: Storm Weaver (Type W), Ceaseless Void (Type V) then Signus (Type S), respectively.
 * This theme contains a motif from The Devourer of Gods' theme.
 * This theme does not play when weakened forms of the Sentinels are summoned after The Devourer of Gods first form is defeated. Instead, Scourge of the Universe will play until all of the Sentinels are defeated.
 * If the Calamity Music add-on mod is disabled, Boss 3 will play for Storm Weaver and Ceaseless Void, and Boss 4 will play for Signus, Envoy of the Devourer.
 * Despite being bosses, none of them have a Treasure Bag.