Escape from Arthas! Mythic Dungeon Quest

[UAtest]

So someone shared this quest with me the other day: "Escape from Arthas!"
It also gave me a "Mythical Stone" in my bag. Says I can use it to change the dungeon to "Mythic Difficulty" and that the quest can only be completed on Mythic Difficulty.

Not sure what to make of it. I think I remember frostmourne having some kind of Mythic dungeon system but never seen it on Icecrown. Am I missing something?
I do not know how to use this stone or where and how to complete this quest.

[jovadoktor]

You probably got it from people that already transfered their character from Frostmourne, i don't think it's possible to complete it on Icecrown tho

[Disktrasa]

It's a Quest from someone who transfered from frostmourne to icecrown and the quest still remained after the transfer so he shared it on Icecrown and now we have a lot of confused people with a epic item called "mythical stone" in our bags, myself included.