Basically the In The Hall Of The Thunder King Achievement is being . doing all the dailies and getting the Arcane Trove /Sunreaver Bounty. List of Removed Content for 7.0?.
I did it! I finally managed to get the entirety of the [In The Hall Of The Thunder King ] achievement in a single.
The Troves of the Thunder King allows you to walk into Lei Shen's treasure vaults, You can kill him for part of an achievement, or let him go. God-Hulk Gulkan (Troves of the Thunder King - Warlock PoV)