Cryogen

"The ancient ice spirits have been unbound!"

Cryogen is a Hardmode boss that can be fought in the Snow or Ice biomes which possesses many phases and features a multitude of projectiles and enemies.

Defeating Cryogen will free the Archmage, as well as generate Cryonic Ore in the Ice biome.

Spawn
Cryogen does not spawn on its own and requires the player to summon it with a Cryo Key while in the Snow biome at any time of day.

Behavior
Cryogen has six phases, each of which has its own attack pattern and AI. It will progress through these phases as it loses health.

Cryogen also spawns with an ice shield which protects it and inflicts contact damage; this shield must be destroyed to directly attack Cryogen and will regenerate seconds after being destroyed. When destroyed, the shield will explode into a cross-shaped burst of 4.

Throughout the fight, it will also summon 2 every 7.5% of its health taken. may have a chance to replace small Cryocores from its third phase onwards, and are able to replace either servants on its fifth phase onwards.
 * Aurora Spirits fly towards the player similarly to Ancient Vision, while Cryocores accelerate towards the player.

Leaving the Snow biome will cause Cryogen to enrage, almost doubling its speed and acceleration.

Phase 1

 * Slowly chases and levels with the player.
 * Fires an evenly-spaced burst of 16 every 2 seconds.

Phase 2

 * Transitions at 80% health.
 * Attempts to fly above the player while continuing to fire bursts of.
 * The amount of Ice Blasts are reduced from 16 to 12 from this phase onwards.

Phase 3

 * Transitions at 70% health.
 * Slowly chases the player but stays slightly below the player.
 * Has a 50% chance to replace the attack with a spread of 6.
 * Ice Shards arc upwards slightly ahead of the player before raining down.

Phase 4

 * Transitions at 55% health.
 * Attempts to fly above the player.
 * Stops firing Ice Blasts, but continues firing spreads of which fly upwards for less time before raining down.
 * The amount of Ice Shards are increased from 6 to 12 during this phase.

Phase 5

 * Transitions at 40% health.
 * Slowly chases the player.
 * Loses the ability to regenerate its shield.
 * Stops firing Ice Shards but resumes firing at double the frequency.
 * Every 5 seconds, Cryogen will teleport somewhere near the player and start attacking again.
 * The location it teleports to is telegraphed by a zone of blue dust 2 seconds before occuring

Phase 6

 * Transitions at health.
 * Stops firing either projectiles for the remainder of the fight.
 * Suddenly picks up speed and begins charging erratically, attempting to ram the player.
 * Its rotation speed will increase when below and even further when below  health.

In Expert Mode

 * Transitions into Phase 6 at 20% health.
 * Regenerates its shield every 12 seconds instead of 16.
 * Every 10 seconds, Cryogen releases a cross-shaped burst of 4, with a 50% chance for it to be rotated 45 degrees.
 * This occurs in all of the above phases alongside other attacks.
 * Ice Bombs explode into a hexagonal burst of 6 gravity-affected after 5 seconds.
 * They also inflict Glacial State for 1 second, Chilled for 1.5 seconds, and Frostburn for 2 seconds on contact.

In Revengeance Mode

 * Transitions into Phase 6 at 25% health.
 * Cryogen and its projectiles are slightly faster.
 * Gains a new phase when below health:
 * Unlike other phases, this does not change its appearance.
 * It launches itself upwards and stays above the player. are no longer fired out every 10 seconds, but  waves are released during this attack.
 * Then, it rapidly charges the player for a total of 3 times before repeating this pattern.

In Death Mode

 * Transitions into Phase 6 and 7 at 30% and 15% health respectively.
 * Cryogen and its projectiles are even more aggressive and faster.
 * 4 waves of are released in its final phase.

Aftermath

 * Once Cryogen is defeated for the first time, Cryonic Ore spawns in the Ice biome.
 * Cryo Slimes will begin to spawn in the Cavern layer.
 * The Archmage will begin to arrive if provided suitable housing.
 * If the Archmage isn't in the player's current world, he will drop alongside Cryogen's loot.
 * The Angry Dog enemy's stats are increased and will start dropping Essence of Eleum.

Tips

 * It is easier to see Cryogen's projectiles during the night.
 * A wide arena with several levels of platforms can help in dodging Cryogen's attacks.
 * Putting a roof of solid blocks above the platforms can help protect you during Cryogen's second phase.
 * Be careful: Building platforms too far above the ground could cause the player to exit the Snow biome and enrage Cryogen.
 * Moving at a constant speed will cause Cryogen to hover in the same place relative to the player, making it an easy target for ranged weapons.
 * Moving slowly enough will cause Cryogen to hover directly above the player, this makes it very easy to hit, but be wary of its ice bombs and it potentially getting up close.
 * Avoid getting hit by Cryogen's Ice Blasts at all costs as they will freeze the player, possibly leading to a swift death.
 * Cryogen's final phase is one of its most deadly. If on Revengeance or Death Mode, saving Rage and/or Adrenaline to quickly finish it off during this phase could be a life-saving decision.
 * In multiplayer, Cryogen does not despawn when off-screen and moves slowly across the map, allowing players to slowly kill the boss.

Trivia

 * Cryogen's theme is Antarctic Reinforcement, which was composed by the artist DM DOKURO.
 * While in production the theme was originally intended to be called "Frostbite."
 * If the Calamity Music add-on mod is disabled, the Frost Moon's theme will play instead.
 * Cryogen was previously an alternative for The Destroyer because of its previous ability to drop Souls of Might.
 * Originally, every time upon entering phase 6, a status message would say "Cryogen is derping out!".
 * There is now a 1% (5% if the day is April Fools' Day) chance that this message is displayed when entering phase 6.