Tome of Otherworldly Venoms

Source
Lei Shen's Burial Troves at the end of Troves of the Thunder King scenario have a chance to contain Tome of Otherworldly Venoms.
 * Speak to Taoshi at the bottom level of the Class Hall to start the Troves of the Thunder King scenario. 1 Key to the Palace of Lei Shen is required for each attempt of this scenario.

Note

 * This is the exact same scenario that was available during Mists of Pandaria.
 * After turning in Vault Ticket or Marin Noggenfogger's Lucky Coin to Marin Noggenfogger, you get a chance to loot up to 3 Key to the Palace of Lei Shen from Sparking Set of Keys hanging on one of the pillars in the Uncrowned Vault.