Dark Grey Helhound

There is one tameable creature with this look.

Dark Grey Helhound
Can Be Tamed
Found in a number of disconnected locations, including: the area north-east of the Theater of Pain; the southern shore of a lake, reached through a tunnel in the south edge of western House of Plagues, in south-east Maldraxxus.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.