Corridor Beings

Corridor Beings are illusionary apparitions that commonly appear to adventurers who stay too long in the Corridor of Layer 7. They take no distinct form and appear differently to everyone, usually manifesting as a shadowy creature with the face of someone the observer is familiar with. They pose no physical harm to an individual with a healthy mind but will attempt to weaken the minds of travelers and cause them to lose their sanity, preying on those who can no longer tell reality apart from illusion and taking them to a mysterious location, presumably killing them.

The Catsnail
The most common explanation for the existence of the Corridor Beings, this theory suggests that they are artificial constructs of the Catsnail created in an attempt to deter explorers from reaching the Hole's core. This theory is greatly supported by the fact that the Catsnail will summon Corridor Being-like apparitions to defend itself from threats, before disappearing.