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 ♥♥♥♥♥♥♥♥ 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.