You must learn a special skill to tame Blood Beasts. It is taught by a Blood-Soaked Tome of Dark Whispers, a guaranteed drop from Zul in the Uldir raid on Normal Mode or above (i.e. not LFR). Once learned, this skill is account-wide.
4 possible appearances:
Location & Notes:
Located in Dalaran (Khaz Algar intro quest phase). Only appears during the Breach intro quest for The War Within, when Dalaran first arrives at the Isle of Dorn and is under siege.