THE BASIC PRINCIPLES OF MULTICLASS RULES

A jerk DM could assert "equivalent creature" to some horse isn't essentially granted to almost everything with a quad of equine legs, the humanoid torso disrupting the "similarity" so zerbra's and unicorns Of course, centaurs no.  But that's a jerk DM.   Mobility won't be a challenge if He's utilizing melee, he'll have to spend ki or face assau