ARC-686 refers to a class of anomalous entities documented in the ARC database. Although unfinished and not yet present in the game, ARC-686 has drawn significant attention from the community due to its cryptic ARC document, titled "DemonDogDocument" in the game files. Despite this placeholder designation, its official name remains unknown.

The ARC document describes ARC-686 using plural phrasing, suggesting the existence of multiple instances. However, the rest of this page refers to ARC-686 as a singular entity for simplicity and consistency with other entity entries.