It seems like a popular recipe of making a terrifying and above all foreign enemy in fantasy books is to
1) take one unconventional / not-previously-encountered steed
2) armor your warrior to resemble an unrelated, unconventional / not-previously-encountered beastie.
Inspired by the *spoilers!* cat-riding ant warriors and the camel-riding elephant warriors from the wheel of time and game of thrones respectively, I present to you a hippo-riding dung beetle warrior. With Morning Star.