Phase spider

Phase spiders are giant arachnid monstrosities that originate from the Ethereal Plane and can transport between that plane and the Material Plane at will.

Appearance
These arachnid creatures are of a pale white and blue color, with spindly legs that reach out to a width of ten feet or more. They have giant dripping fangs and rows of beady red eyes.

Abilities

 * Senses: Darkvision.
 * Attacks:
 * Bite: The phase spider can make a bite attack that deals piercing damage and additional poison damage (conditional on a saving throw).
 * Ethereal Jaunt: The phase spider can move between the ethereal plane and the material plane in either direction as a bonus action.

Known Phase Spiders
Vox Machina encountered several phase spiders in the Hall of the Exalt, a vault beneath the Platinum Sanctuary.

The Mighty Nein encountered a phase spider in the sewers of Zadash.