Reaper

Reaper dogs are known to be the familiars of powerful warriors and spellcasters. Though they can never be trusted as they constantly seek to fill their 'owner' with magic and power in order to flip the coin on who is the master and the familiar... upon enough weakness being shown, a Reaper dog will never hesitate to kill their master and search for a stronger one.
Precious little is known about Reaper dogs beyond this.
Fenbalar Leoris, upon researching, learned the Reaper Hounds were actually former leaders of a cult of personality and ego known as The Trine who were punished for their hubris and arrogance by being transformed into their abyssal hound states.