Ban’thalos is one of the many challenge tames added back in patch 4.2. This level 85 spirit beast can be found in Hyjal, circling high above the Sanctuary of Malorne (around 28,62). The challenge to this tame is the sheer height Ban’thalos spawns at. You need to be able to get aggro and land on solid ground without killing yourself.
There are a couple of ways to pull off the tame, but first you need to have progressed the Hyjal quest lines up until you’ve unlocked the Molten Front daily quest area. If you haven’t yet, this quest will be available on your city’s “call to arms” board. Ban’thalos will be outside of your phase until you do this, along with Magria and Ankha who are also nearby.