Grims......usually taking the form of a black dog act as guardians of cemetaries..Especially fond of it's young charges... the Grim may appear as a friendly companion, or if challenged, a protective adversary.

Perhaps taken from the very early practice of burying an animal as protection in a cemetary as the first interment in hopes that the spirit would therefore keep grave robbers at bay.

Though the above explanation is certainly not within the UnSeelie realm....., the Shapeshifting Grim is indeed a character that you might encounter there....