So awhile ago, I read a fic or series of fics on AO3 where the brothers Winchester accidentally summon a hellhound. I believe an accidentally-magical doily is to blame. The hellhound is ridiculously affectionate and petlike and basically adopts the boys. The hellhound may or may not be capable of teleporting, and its farts smell like lavender (a scent to which Dean has a violent aversion). The boys order the hellhound to look like a normal dog, and it winds up looking like a textbook-perfect Rottweiler, or something. At some point they nearly get in trouble because they have the dog in public without a leash, collar, or tags. At some other point they have to enter the hellhound in a dog show as part of their cover.