Eye of Tyr

The ability Eye of Tyr is attached to the Protection Paladin artifact weapon [item=128866], and can be used as a combat ability when equipped at any time.

HOWEVER - there's also a secondary use of the ability. On the Broken Isles, a few different locations have demons disguised as regular NPCs. These NPCs can be spoken to, and often say something suspicious in response.

When Truthguard is equipped near one of these demons, however, it begins to radiate a holy glow and - after a moment - a button will appear above the action bars prompting you to use the artifact's Eye of Tyr ability. If you're close enough to the demon (which you should be if you have the Eye of Tyr button prompt), using Eye of Tyr will trigger Truthguard's hidden effect [spell=181387].

[spell=181387] will knock the disguised demon down and reveals their demon form, allowing you to fight and kill them. You'll also occasionally you'll hear NPCs nearby commenting on their formerly-disguised comrade suddenly being revealed as a demon.

Currently have found a few disguised demons that can be revealed in this way:

Dareer at Hemit Nessinwary's camp in Highmountain: [npc=109062]

Batmaster Claud at the Forsaken camp at Dreadwake's Landing in Stormheim: [npc=109133]

Horkus at Shackle's Den in Azsuna: [npc=109029]

Lord Adder in Dalaran: [npc=108938]

Astry Fallenbough at the Temple of Elune in Val'sharah: [npc=108978]

Maxwell Caprina in Bradensbrook in Val'sharah: [npc=108964]

Malefica in Sylvan Falls, Highmountain (Aviana's Shrine): [npc=109155]

Armond Thaco in New Dalaran: [npc=108628]

Houndmaster Payne in Greywatch, Stormheim: [npc=109089]

Holk the Wanderer in Thunder Totem (top floor, SW side outside): [npc=109161]

The revealed demons will occasionally drop some Order Hall resources and Artifact Power.

I am a lvl110 Prot Pally ilvl 779 and every time I call Lord Adder out, all I get when he is dead is Sticky Volatile Substance! Nothing else, Not even Resorces! Kinda upsets me that he is that lvl and Elite and drops an item worth about 21 silver and nothing else for me. I have called him out multi-times (approx. 20) using Eye of Tyr when it pops ( The Light Reveals). Does this happen to a lot of peeps or am I just that unlucky?

This extra action button continues to work for me after legion is over as well. It pops up when you are near something that can be activated with it even though your artifact weapon had the juice sucked out of it.