John Winchester encountered a Black Shuck in "Supernatural: Origins" issue #2. He was first given a fang of the creature when Missouri Mosley pulled it from a dead woman's corpse. Missouri claimed that the fang belonged to the creature that killed John's wife, Mary Winchester.
A man posing as Fletcher Gable explained to John a little about the fang and the creature itself. He said it is called a Black Shuck which is like an over-grown Hellhound. The fang is carved with magical sigils. The imposter stated that "shuck" comes from "scucco," an Anglian legend several hundred years old. The Black Shuck usually lives in graveyards lurking in the corners or shadows wherever there are Dead. They can be found in emptied graves or crypts. The man implied that these hounds are guards to the Devil's Gates, places where creatures can pass between realms.
The man told John that the last sighting he heard of was in Eureka, California in a cemetery off Route 101. John headed for that cemetery and had a personal encounter with a Black Shuck. Unfortunately, his brother-in-law Jacob who had followed him, was killed by the beast.
One of the various creatures locked away in a box for several years until it was released in the arch Happily Ever After.