Ceaseless Void

The Ceaseless Void is a post-Moon Lord boss and is one of the Sentinels of the Devourer. It drops Dark Plasma, which is a crafting material required to craft the Cosmic Worm.

Spawn
The Ceaseless Void does not spawn on its own and requires the player to summon it by using the Rune of Kos in the Dungeon.

Behavior
Unlike most other bosses, the Ceaseless Void has very little health, but compensates with massive damage reduction (DR). This effectively allows it to only take 1 or 2 damage from any attack when vulnerable. The Ceaseless Void constantly floats toward the player to deal contact damage, its motion slightly affected by momentum.

Upon being summoned, the Ceaseless Void is completely invincible to damage, and Dark Energies are spawned in three groups, each group having their own distinct behavior. The only way to render the Void vulnerable to damage is to destroy the Dark Energies it spawns. The Ceaseless Void will return to its invulnerable state and spawn more Dark Energies after reaching 70% health ( HP), 40% health ( HP), and 10% health ( HP) respectively. Dark Energies become immune to knockback when below health.

The Ceaseless Void also releases a laser portal every seconds, which homes in on the player and fires 8 homing lasers every 3 seconds before dispersing 10 seconds after its initial summon. The lower its health, the more frequently a laser portal is spawned.

When below 90% health, the Ceaseless Void will begin to violently suck the player towards itself if they get too close. The area in which the player will be sucked in can seen through a ring effect that periodically appears around the Void, with each appearance indicating a pulse of gravitational force. This area gets larger as the Ceaseless Void loses health.

The Ceaseless Void detects nearby active tiles in a 40x40 area around itself. Its fire rate, projectile lifespan, and damage increases the less active tiles are around it, up to a maximum of quadrupled fire rate, 80% more lifespan, and 40 increased damage with no tiles at all.

If the player exits the Dungeon during the fight, it will enrage, causing its maximum speed to drastically increase and its gravitational area to moderately increase in overall size.

In Expert Mode

 * The Ceaseless Void summons laser portals more often.
 * Dark Energies are more aggressive.

In Revengeance Mode

 * The Ceaseless Void summons 24 Dark Energy projectiles instead of 12 in the second, third and fourth iterations of its pattern.
 * During the laser portal attack, the Ceaseless Void additionally summons a set of four invincible Dark Energy projectiles, which orbit around the spot they're spawned from for 10 seconds. The size of the orbit varies between each of the projectiles, and they will disappear shortly after being spawned.
 * While Ceaseless Void is below 50% health, or enraged, this attack is replaced with a ring of twelve invincible Dark Energy projectiles.
 * Dark Energy swarms are larger and are more aggressive.
 * Dark Energies become immune to knockback at 70% health instead.

In Death Mode

 * Dark Energies are even more aggressive.
 * Dark Energies become immune to knockback at 90% health instead.

During the Boss Rush

 * All difficulty mode changes, regardless of the world's difficulty mode.
 * The Ceaseless Void's maximum speed is drastically increased, as if enraged.
 * Unlike the normal enrage, its gravitational area is not affected.
 * Dark Energies are always immune to knockback.

Resistances

 * All Dark Energies take reduced damage from non-minion piercing projectiles in Expert Mode. Projectile damage is divided by the number of times it pierces. Infinite piercing deals 50% damage.
 * All Dark Energies reduce damage from grenade-type projectiles by 80%. A list of affected projectiles is below.

Tips

 * Clearing out a large area in the Dungeon prior to the fight will greatly help. When expanding, Dungeon Walls Unsafe may help to ensure that the player is always considered to be within the Dungeon, so that the Ceaseless Void does not enrage.
 * Single-shot projectiles that deal high damage and slow weapons with high damage are ineffective against the Ceaseless Void, as it will only take one damage per hit. Use fast-firing weapons to maximize your number of hits and thus DPS.
 * Bring high damage weapons especially if they have area of effect capabilities, as they can easily clear out the Dark Energies.
 * Use a weapon with very high knockback to keep Dark Energy swarms at bay. This will make it easier to group them up and stay away from them.
 * The Ceaseless Void will not attack the player during its vulnerable state if the player is under blocks. Hide under blocks to give yourself a breather to heal or build up Adrenaline.
 * The Elemental Disk can produce many splitting projectiles, allowing it to easily take out the swarms of Dark Energies.
 * The Elemental Eruption will take out the Ceaseless Void incredibly quickly, but is not very strong against its minions.
 * The Phantasm with Luminite arrows can deal a lot of damage to the Ceaseless Void. This is especially recommended if fighting the Ceaseless Void before Providence, the Profaned Goddess.
 * If Storm Weaver has been defeated, The Storm is very effective both versus the Ceaseless Void and its Dark Energies.
 * The Starfleet can deal massive damage while the Ceaseless Void is vulnerable, sometimes skipping phases or killing it instantly. If aimed well, it can dispatch Dark Energies in a single shot.
 * The Telluric Glare is very useful for the Dark Energies and can skip sometimes 1 or 2 phases.
 * The Nuclear Fury does excellent damage to clumped together Dark Energies and does decent damage to the Ceaseless Void itself.
 * The Blissful Bombardier is a good choice against the Dark Energies for its homing and area damage. Its decent fire rate can also deal with the Ceaseless Void itself pretty easily.
 * The Ark of the Elements is still a good choice, as it homes in on the Dark Energy and the Ceaseless Void.
 * The Divine Retribution's storm of spears will deal extreme damage to the Ceaseless Void when it is vulnerable.
 * Single-target minions struggle against the Ceaseless Void due to its many minions. Use summons with an area of effect damage such as the Stardust Dragon Staff or Elemental Axes instead. The Profaned Soul Artifact is also recommended.
 * The Molten Amputator's explosions and lava globs can deal with grouped Dark Energies very rapidly.
 * If the player is having a very hard time making space in the Dungeon, they could lure the Ceaseless Void out of the Dungeon if they can handle it being enraged. This trades a lack of space for a large increase in speed for the Ceaseless Void.
 * The player can make use of Asphalt Blocks to move faster or blocks like Frozen Slime Blocks and Ice Blocks to conserve momentum. The Slime God's lore item can also help if paired with Asphalt Blocks.

Trivia

 * The Ceaseless Void's theme is a segment from Servants of the Scourge, which was composed by the artist DM DOKURO.
 * This theme contains a motif from The Devourer of Gods' theme.
 * If the Calamity Music add-on mod is disabled, Boss 3 will play instead.
 * Despite being a boss, the Ceaseless Void will not drop a Treasure Bag in Expert Mode.
 * The Ceaseless Void has the lowest health out of all bosses, but this weakness is nullified with having the highest DR.