Abyssal Echoes[1] are agents of the Abyss, with Dredge being able to summon them if needed, as revealed in the voice lines of the Abyssal Echo skins. The canonicity of Abyssal Echoes is unclear, though based on a dev statement, it appears the concept of Abyssal Echoes are canon, while the various skins aren't literally canon Abyssal Echoes.
Known Abyssal Echo Skins[ | ]