It’s like a mix between an equestrian centaur and a classical one. Like they put a realistic prosthetic on his nose to make him look like something not out of place in FiM. Nothing this humanoid exists in main series, even Iron Will is “feralized” for lack of a better term for what he allegedly represents. Very good looking work on his head and facial features that doesn’t look slapped on, like it could either stay or be removed when he’s done. Tirek is a centaur as far as having six limbs, but having ape like upper body features. Then bovine ones.
 
Moreover, he reminds me of an Andalite from the Animorphs series, the rough looking tail especially. The most notable feature however would be his lack of a mouth, and he has one.