Slate

Once no more than a small pink faerie dragon, Slate was plucked from his life as a non-sapient animal and ascended. He served as a conduit between the mysterious Grey Patron's magic and whatever vessel he had chosen to serve him – until he ended up with Cas.

At first she wanted nothing to do with him, but slowly she warmed up until they shared a bond nigh unbreakable.

Slate is generally optimistic and upbeat, the foil to Cas' serious pessimism. But he's not very powerful on his own, so he usually shies away from combat.