Bonehoof Tauralus

There are quite a few reasons that you do not want to stand behind a tauralus, the hooves and whip-like tails being the least of them.

Riding Requirements:

This mount is available to all eligible characters on your account.
Level 10
Apprentice Riding
Necrolord Covenant only

Source:

Tahonta in Maldraxxus.

Notes:

This mount can only be looted by members of the Necrolord Covenant who have their Abomination Factory upgraded to rank 2, and have the construct "Neena" as their companion when they kill the rare Tahonta. Even then, the drop doesn't appear to be guaranteed. Tahonta patrols a field to the south-west of the Theater of Pain.