Given that Breaching the Tomb is (finally) account-wide, I decided to hop on my warlock who had finished the campaign to get that sweet, sweet mount. However, there’s supposed to be an NPC in Broken Shore near Deliverance Point to start the chain, and there clearly is not. I have tried manually /tar him as well as confirmed that Trivial Quests are being tracked. I also logged onto my main, who was the first to get the achievement, and then back to my warlock without success.
The NPC in question is Mor’zul Bloodbringer, and the original guide I have for it says he’s directly in the class hall, so I went there first and he does not have dialog options for me. Then, Wowhead notes said he was at Deliverance Point, so I went there, and this is where I’m stuck. He isn’t here at all.
Also, the Achievements pane says that my alt does not have credit for the achievement.
I noticed it is not showing credit in my achievements yet either, which is probably a bug in some regards, but keep in mind you still have to do a quest chain to recruit your final champion prior to doing the mount chain. I haven’t done this entirely yet on any character, but my mage went back to her hall after only doing a few parts of “breaching the tomb.” There, she did a quest to empower her artifact weapon, then went back to Broken Shore and got the quest to recruit a champion (I think from Maiev), which usually doesn’t show up until you’ve done the “breaching the tomb” questline. Then back to the hall to start that, which is usually a substantial quest chain so I haven’t finished yet to give an account on the entire experience. I believe after that, the mount chain should appear.
I even got the achievement for unlocking the heroic skins of my artifact weapons.