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Mana-Tombs will be making its return to current content via the Timewalking system introduced with Patch 6.2.  All players level 71 and above will be able to queue for the Timewalking version using the LFD tool when the special event is active.  The official highlights blog is here.  Don't forget to pick up A Burning Path Through Time.

Note:  The Eye of Haramad does work in the Timewalking difficulty.  (The key allows access to an extra boss named Yor.)  You will need to complete quests and grind your way to Exalted with The Consortium in order to acquire the key.  See The Eye of Haramad (quest) on Wowpedia.