Astrum Aureus

"A titanic cyborg infected by a star-borne disease..."

Astrum Aureus is a Hardmode boss. Defeating it causes an Astral Infection meteor to fall somewhere in the world.

After defeating the Moon Lord in Revengeance Mode or Death Mode, Astrum Aureus increases substantially in difficulty, with boosted health and damage, and drops a new mount.

Spawn
Astrum Aureus does not spawn on its own and must be summoned at Night using the Astral Chunk in the Astral Infection biome.

Behavior
When first summoned, Astrum Aureus will start in its recharging phase. While recharging, Astrum Aureus will deal no contact damage and has no defense. Once its flames ignite, Astrum Aureus will begin to attack the player and cycle through its attack pattern. At the end of each cycle, it will stop moving and enter its recharging phase again. All attacks inflict the Astral Infection debuff.

If Astrum Aureus is alive when it becomes daytime, it will enrage, moving faster and jumping significantly farther.

Attacks

 * Crawls around on the ground and periodically jumps into the air above the player in an attempt to crush them or get on level ground with them, getting more aggresive as its health decreases.
 * Its jumps scale in height based on how high the player is and will attempt to intercept them if they're moving.
 * Shoots bursts of lasers directly at the player, firing them faster as its health decreases.
 * At 50% health Astrum Aureus also:
 * Launches three consecutive waves of eight from itself in every direction, which fly some distance before homing in on the player. These projectiles gain increased speed and homing when the player is near them. Astral flame crystals will lose their homing capabilities after six seconds and will fly offscreen.
 * Teleports near the player, this happens shortly after the crystals are fired.

In Revengeance Mode

 * Can fire one wave of astral flame crystals above 50% health.
 * Summons a pair of Aureus Spawns; they are initially passive, but will become homing bombs if they take enough damage, which explode in 10 seconds or upon hitting a tile.
 * Once the Moon Lord is defeated, Astrum Aureus's health and projectile damage become buffed.
 * Can jump through tiles.

In Death Mode

 * Crawls faster and jumps more aggresively.

Aftermath

 * Once defeated, the Wizard begins selling Astral Chunks.
 * Another Astral Meteor will spawn in the world (under the right conditions).
 * The Drunk Princess will begin selling Everclear, the Star Beam Rye at night, and the Bloody Mary during a Blood Moon.
 * The Astral Chest will be unlockable in the Dungeon.
 * Several Astral Infection enemies will drop unique items:
 * The Mantis will now drop the Astral Scythe.
 * The Atlas will now drop the Titan Arm.
 * The Nova will begin to drop the Stellar Cannon.
 * The Aries will begin to drop the Stellar Knife.
 * The Astralachnea will begin to drop the Astralachnea Staff.
 * The Astral Slime will begin to drop the Abandoned Slime Staff.
 * The Hive will begin to drop the Hive Pod.
 * The Hadarian will begin to drop Hadarian Membranes.
 * The Stellar Culex will begin to drop the Starbuster Core.
 * Astral Crates will contain Aureus Cells, Astral Injections, Gravity Normalizer Potions, and several items dropped by Astral Infection enemies.

General

 * Moving in a semi-circle around Astrum Aureus while it fires lasers can help the player successfully avoid them.
 * The astral flame crystals gain increased velocity and homing capabilities the closer they are to the player, making it essential that the player keeps their distance from them until they launch away.
 * In Revengeance Mode, avoid damaging the Aureus Spawns. They are initially harmless and will only attempt to harm the player if they take enough damage.

Trivia

 * Astrum Aureus's theme is Interstellar Stomper, which was composed by the artist DM DOKURO.
 * If the Calamity Music add-on mod is disabled, Boss 3 will play instead.
 * Astrum Aureus replaces a removed boss, the Astrageldon Slime, which was a boss that fought much like the King Slime but was twice as big and emitted lasers in bursts at the player.
 * Prior to Interstellar Stomper's implementation, Astrum Aureus's theme was Cosmic Disgust, which was originally intended for the Astrageldon Slime. This is why the theme's introduction contains a motif from The Slime God's theme.
 * Astrum Aureus's name roughly translates to "golden star" in Latin, although its name is actually a reference to an infectious bacteria named Staphylococcus aureus.
 * Astrum Aureus's design was inspired by Security Robot B.O.X. from Metroid Fusion, as both their appearance and movements are similar, and are also both cyborgs that have been infected by a space infection.