Havoc / Twinblades of the Deciever Hidden AppearanceThe hidden appearance for the Twinblades of the Deciever is called Deathwalker, and unlocked with the item Guise of the Deathwalker. To start the quest chain to get this item, you firstly need to complete the Order Hall questchain. Once that is done, you can find a random item drop called Candrael's Charm, which can drop from pretty much any mob on The Broken Isles.
Once you find this, go to Felsoul Hold and look for Candrael Twinshadow and talk to her. This will allow you to fight a demon called Downfall, which you must kill. This fight can be kind of tricky, because you need to stay away from the winds he create. However, once you manage to kill him, you can loot the Guise of the Deathwalker and unlock your Deathwalker appearance.
Deathwalker color tints:Default: Yellowish.
Green: Complete 100 Dungeons with Deathwalker equipped.
Purple: Complete 200 World Quests with Deathwalker eqipped.
Red: Kill 1000 enemy players with Deathwalker equipped.
Vengeance / Aldrachi Warblades Hidden AppearanceThe hidden weapon artifact appearance for Vengeance / Aldrachi Warblades is called the Iron Warden, and is unlocked with the item called Bulwark of the Iron Warden.
In order to get this item, you firstly need to do the Order Hall Advancement called Twisting Nether, allowing you to use a portal to get into the Sanctum Crystal. There you can use a book to summon a demon one level above the summoner, and this demon has a chance to drop the Bulwark of the Iron Warden. You can only get loot from one demon each day, so if you don't get the item, keep doing this event each day until it drops.
The exact drop chance is still not known.
Iron Warden color tints:Default: Green.
Blue: Complete 100 Dungeons with Iron Warden equipped.
Purple: Complete 200 World Quests with Iron Warden eqipped.
Red: Kill 1000 enemy players with Iron Warden walker equipped.