A bygone is a creature of myth and legend that can no longer exist openly on Earth due to its incompatibility with the Consensus. The rarest and mightiest of the bygones cannot exist on Earth at all, only in the Umbra; their very existence is incompatible with the Consensus, and they accrue paradox while on Earth. Bygones are not to be confused with Umbrood or other spirits, which are Umbral creatures formed wholly of spirit, or with chimerae, which are creatures of the Dreaming.