Black Cloud Serpent w/ Dark Sheen

There are 2 tameable creatures with this look.

Black Cloud Serpent w/ Dark Sheen
Requires Cloud Serpent Taming.Cloud Serpent Taming
You must learn a special skill to tame Cloud Serpents, which is different to the skill required to tame other Lesser Dragonkin. Pandaren hunters gain the skill automatically, but hunters of other races must learn it from the tome How to School Your Serpent, which may purchased from San Redscale at The Arboretum in The Jade Forest. You require Exalted standing with The Order of the Cloud Serpent to read this tome, but the learned skill is account-wide. You can even purchase and read this tome on a non-hunter character.
Lesser DragonkinLevelLocation
Can Be Tamed
Mount Neverest, Kun-Lai Summit
Retains its original name after taming.
The Wild Onyx Serpent circles Mount Neverest in Kun-Lai. It can be difficult to reach but you can just get in range of it if you find the right outcropping to stand on. At max level, use an item level 1 weapon (can be bought from a weapon vendor), remove your armor, and perhaps even kill yourself and take resurrection sickness to pull the serpent without killing it.
Can Be Tamed
35Shan'ze Dao, Townlong Steppes
Accompanies Shan'ze Serpentbinders.
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.

Matching Mounts

Matching Companion Pets