Eidolon Wyrm

Eidolon Wyrms are mini bosses that spawn in the 3rd and 4th layers of the Abyss. They are initially passive and will not attempt to hurt the player. However, if the player deals damage to them, they will become hostile and attack the player with contact damage or magic projectiles.

Behavior
The Juvenile Eidolon Wyrm spawns in the third and fourth layers of the Abyss at any point in the game. Its roar will alert the player that it is nearby and is hunting them. Once hostile, it will chase the player on sight until they leave the biome, though its size makes it difficult to maneuver around. It will summon balls of ice which fire ice shards in every direction, and summon orbs that unleash streaks of lightning at the player. It also possesses telekinetic abilities which allow it to throw the player in any random direction, accompanied by a loud sound and a burst of blue sparks.

The Adult Eidolon Wyrm spawns in the same two layers after Polterghast has been defeated, but is much rarer. It will also spawn at any time if a player is affected with the Chaos State debuff (given by Rod of Discord, Normality Relocator, and similar items) while in the Abyss, giving the message "Eidolon Wyrm has awoken!" The adult behaves similarly to its juvenile counterpart, although it is very large, moves much faster, deals far greater damage, and is incredibly resilient to damage to the point of nigh-invincibility. Like its juvenile counterpart, it has the ability to periodically fling the player in a random direction through telekinesis, although its telekinetic attack is far stronger. No more than one Adult Eidolon Wyrm can exist at once.

Eidolon Wyrms inflict the following debuffs in Revengeance Mode:
 * Crush Depth for 20 seconds (Head)
 * Electrified for 2 seconds (Lightning)
 * Frozen for 1 second (Ice Ball/Shards)
 * Chilled for 2 seconds (Ice Ball/Shards)
 * Frostburn for 4 seconds (Ice Ball/Shards)

Trivia

 * When the Adult Eidolon Wyrm is provoked, it will make a similar sound to the start of the unused theme Threats of the Ocean Floor by DM DOKURO.
 * Furthermore, this theme was designed to be used with the Abyss mini bosses including the Eidolon Wyrms.
 * An eidolon in Greek Literature is a spirit-like image of a person, either living or dead.
 * Their ice and lightning attacks are similar to those performed by the Lunatic Cultist. The juvenile's ability to drop the Lunar Cultist Robe and Hood, as well as "Eidolon" being a term used to describe something idolized (potentially in the fashion of a cult), further establishes a connection between these enemies.
 * They may also be related to the Eidolist, as they have similar names and drops, and they both spawn in the Abyss.
 * Its design is based on a creature from the aquatic exploration game Subnautica, known as the Ghost Leviathan. The original sprite was also a copy of the Ghost Leviathan's design.
 * The different life-stages makes this more evident because there are both juvenile and adult Ghost Leviathans.
 * The Adult versions of both creatures share the similar purpose of preventing the player from doing something (Adult Ghost Leviathans protect the crater edge, while the Adult Eidolon Wyrm prevents the player from using the Rod of Discord or other short ranged teleportation items).
 * The Adult Eidolon Wyrm could be considered the Calamity Mod version of the Dungeon Guardian since both are extremely strong enemies that are intended to prevent the player from performing a certain action.
 * Prior to the 1.3.4.001 update, the Adult Eidolon Wyrm had the highest health of any NPC in the mod, with a whopping 30,000,000 health.