Beast Mastery Hunters can finally tame Rezan, the Atal’Dazar boss, on live servers!
Your Hunter must know how to tame Undead via 
Simple Tome of Bone-Binding. The tome is a random drop from mobs in Maldraxxus (Shadowlands) with Ol’ Big Head (58,54) having the highest drop chance.
You can also run this macro to see if you can tame Undead.
Comment
byu/Bandicoot733 from discussion
inwow
Undead Hunters can tame Undead pets by default without needing the tome. If you plan on working on getting the tome with a fresh Hunter that just got to the Shadowlands, you must first pick a Covenant to leave Oribos.
