Step 1 : Introduction to the question "5. He was brother to the hell gate guardian Orthrus, at least according to Greek mythology. He had a distinctive physical appearance and it was a Herculean task to bring him to heel. Which monstrous dog am I describing?"
...1. Canis 2. Bran 3. Barghest 4. Cerberus In Greek mythology Cerberus was the gigantic hound which guarded the gates of Hades. He was described as a three-headed dog with a serpent's tail, a mane of snakes, and a lion's claws. One of the extra clues I embedded in the question referred to a Herculean task. This was because one of the twelve 'Labours of Hercules' was to fetch Cerberus from the underworld.