Hunter Long Legs

Hunter Long Legs is a rare creature in the Downpour DLC, which spawns under specific requirements exclusively while playing as.

Appearance
Hunter Long Legs takes the appearance of a reanimated corpse overtaken by a mass of flesh-coloured tendrils, similar to the Rot(⋅⋅).

Spawning
Hunter Long Legs spawns only when playing as, if the player has failed a run on the same save slot. It then spawns in the same room as that run ended.

Trivia
It can be assumed that this is what happened when hunters time "ran out" as stated by LttM