There is no requirement to have killed Archimonde on Heroic before entering Mythic. Restrictions like this have existed in the past, but they were easily bypassed by inviting any player who had killed the boss on Heroic.
The old Shattered Halls could have a Prot Warrior tank who has no AoE threat, just tab Sundering. Situations like that made the dungeons more challenging. Most people didn't have AoE and AoE threat, so tanks couldn't hold threat on all of the mobs at
Iron - -Fix Righteous Fury so it doesn't unapply by entering and exiting a dungeon. Most buffs are cleared when entering Timewalking, similar to Arena. This is necessary to ensure that the down-scaling that occurs when you enter the dungeon is done c