Honoring the Past

/run local _,_,_,a, b = GetAchievementCriteriaInfo(11230,1) print("Frost Hidden Appearance: "..a.."/"..b)
Just /kneel in Lordaeron's Room. -This is located in Undercity.

/run local _,_,_,a, b = GetAchievementCriteriaInfo(11231,1) print("Unholy Hidden Appearance: "..a.."/"..b)
Summon 2000 undeads (via Apocalypse, Army of Dead, etc) -Best way to fast track this is entering Proving Grounds, start a challenge, summon your Army of Dead, yield/fail the trial, the 10 minute CD resets. Rinse and repeat.

/run local _,_,_,a, b = GetAchievementCriteriaInfo(11229,1) print("Blood Hidden Appearance: "..a.."/"..b)
Hit 1000 enemies with Consumption. -Best way to fast track this is head to Firelands, right before Lord Rhyolith farm the Unstable Pyrelords (they spawn infinitely and you can cleave 50+ per cooldown.)

The /run codes will tell you your progress on all three when copied and pasted individually.

Is this an actual achievement you can unlock in-game?

Seems that this achievement is hidden. You can check it i.e. using Overachiever addon and search by achievement id (11143). For me it says that I got it 17.02.2017, and same was said by GM in the ticket I created. Also, GM explained that "This achievement is not displayed in the standard game interface.". So seems that it is a tricky hidden achievement now :)