Now that Molten Core is available in Season of Discovery, Rogues have been happy to finally uncover the secret to their exclusive weapon, the Shadowflame Sword!
Not only does Shadowflame Sword have a great effect and some excellent stats, but it looks pretty cool too! When you activate Blade Flurry you are 'engulfed in Shadowflame' giving your character a great visual effect, as seen in this video below from SimonizeShow.
Rogues can aquire this sword by combining Implacable Blackguard and Shadowflame Skull.
The Shadowflame Skull has so far been confirmed to drop from Majordomo Executus in Molten Core and has a small clue in the text, pointing you toward your next step.
To obtain Implacable Blackguard, you must first either reach Exalted with the Thorium Brotherhood and craft Blackguard with Blacksmithing or purchase Blackguard from a Master Swordsmith.
The materials required to craft Blackguard are:
This sword can only be crafted at the Forge of Lord Incendius in Blackrock Depths.
Once you have Blackguard you then must reach Honored with the Thorium Brotherhood and exchange this, along with 25 Firelands Ember and 2 Lava Core for Implacable Blackguard.
You can reach Honored with the Thorium Brotherhood while collecting Firelands Ember by completing the Blackrock Eruption Event Dailies.
Once you have earned the Implacable Blackguard, and looted the Shadowflame Skull from Molten Core, you simply need to combine them by right-clicking on Shadowflame Skull in order to create your new Shadowflame Sword!