The Eidolon Wyrm is a mini boss that spawns in the 4th layer of the Abyss and is also summoned by the Primordial Wyrm during its first four phases. It is initially passive and will not attempt to hurt the player until it is damaged, at which point it will become hostile and attack the player.
The Eidolon Wyrm spawns in the fourth layer 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 until either it or the player is killed.
The Eidolon Wyrm is an aerial worm-like enemy with 42 segments in total. Its body and tail segments can neither take damage nor deal contact damage. It is initially passive until it has been struck or if the player has the Chaos Statedebuff, and also if the Primordial Wyrm is alive. When hostile, it screams and actively chases the player similarly to a Wyvern. The player is inflicted with Crush Depth for 5 seconds upon contact with the head.
Notes
The body segments of Eidolon Wyrms are intangible, dealing no damage to the player and having complete immunity to attacks. Only their heads are capable of dealing or receiving damage.
Being affected by Chaos State causes any living Eidolon Wyrms to instantly discover the player and begin attacking.
The Eidolon Wyrm will not spawn in the 4th layer of the Abyss if a Colossal Squid or Reaper Shark is already present.
It can home in on players, even when not hostile. However, they don't deal contact damage when passive.
In the Get fixed boi seed, it plays the Sunskater squeak sound instead of its usual roar sound.
Trivia
The Bestiary entry for the Eidolon Wyrm: "Relatives of the auric dragons, they adapted to hide away in a forgotten corner of the world to survive the great purges. And yet even without auric souls, the power of eidolon wyrms rivals many of their brethren who possessed them."
An eidolon in Greek Literature is a spirit-like image of a person, either living or dead.
"Eidolon" is a term used to describe something idolized (potentially in the fashion of a cult), which establishes a connection to the Cultists.
They may also be related to the Eidolist, as they have similar names and 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.