The Black Dog is a ghostly hellhound who is said to consume darkness. He has not appeared as an enemy in the Castlevania series, but the Black Dog DSS card and its associated Summon Black Dog spell make an appearance in Castlevania: Circle of the Moon.
The Black dog is a spectral or demonic entity found primarily in the folklore of the British Isles. It is essentially a nocturnal apparition, some of them shapeshifters, and are often said to be associated with the Devil or described as a ghost or hellhound. Its appearance was regarded as a portent of death. It is generally supposed to be larger than a normal dog and often has large glowing eyes. It is sometimes associated with electrical storms (such as Black Shuck's appearance at Bungay, Suffolk) and also with crossroads, places of execution and ancient pathways
- Even if it's not called "Black Dog", the Shadow Wolf of Castlevania: Lament of Innocence could possibly be a variation of the Black Dog.