Ultranium/Erebus

"Darkness Overruns the world..."

Erebus is a Post Moon Lord intended to be fought after  and is currently one of the final bosses of the Ultranium mod.

While Erebus is alive, the music will play.

Summoning
Erebus can either spawn from a massive vortex at the end of the event, or it can be summoned manually by using the  during the event.

Behavior
Erebus behaves like a massive worm enemy, flying through the air and digging through blocks while trying to ram into the player. Each of its body segments can only be hit once roughly every second, with all attacks during this period beyond the first dealing massively reduced damage.

Phase 1
It will periodically perform additional attacks while chasing, cycling through them in order:
 * Fires three spreads of black spit blasts at the player.
 * Releases a large number of dark tentacles from its body segments that extend towards players before vanishing.
 * Rapidly lunges at the player 3 times. This is telegraphed by its head glowing teal, its jaw opening wide, and its movement significantly slowing for a few seconds.
 * At 75%, 50%, and 25% health, Erebus will temporarily go invincible, stop using special attacks, and spawn a teal portal near the player, which periodically fires bursts of blasts around itself. After a few bursts, a ring of particles is emitted and Erebus teleports and charges from the portal.

Phase 2
Below 50% HP, Erebus will lose all attacks from the previous phase and switch them out for new ones. These will be performed on a timer in a fixed order.
 * Summons many rings of teal spikes around the player. After a brief delay, these rings turn into damaging runes that explode into plus-shaped bursts of black fireballs.
 * Pauses as its head glows purple, roars, and launches a large purple vortex at the player, which homes in on them and deals constant contact damage before exploding into a ring of returning shots.
 * Fires six homing spike balls at the player.
 * Breathes a massive stream of teal flames from its head while chasing the player.
 * After its head glows for a moment, teleports far beneath the player and waits for a second before dashing straight upwards at incredible speed, firing walls of spit projectiles perpendicular to its movement. This attack will leave it very high up in the air and force it to fly back down.

Phase 3
At 33% HP, Erebus will summon a ring of five Restless Souls with 6,500 HP each that orbit its head while firing black projectiles. Erebus is invulnerable until all the Restless Souls have been destroyed.

In addition, in between its purple vortex and spike ball attacks, Erebus will rapidly circle the player for several seconds while firing a large number of spit blasts inwards.

Phase 4
Below 20% HP, Erebus discards all prior attacks besides his circling attack. He then exclusively alternates between the circling attack and lunging five times at the player with a much shorter telegraph.

Defeating Erebus will instantly end the Abyssal Armageddon if it is currently active.

Trivia

 * In Greek mythology, Erebus was the primordial embodiment of darkness, often depicted as one of the first beings to come into existence. It was also sometimes used as a name for a region of the underworld.
 * In previous versions of the mod, there used to be a Blood Moon version of the boss, it was eventually removed in the 1.2 update.
 * The blood moon version of the boss was also planned to return in the upcoming 1.3 update of the mod with an exclusive name: "Thanatos". However, it's been decided by the developers that Thanatos is going to be replaced with something else entirely.
 * In Greek mythology, Thanatos was the personification of death.