Guys last week we killed 6 boss on hc did spine normal and progress on dw heroic.(we killed spine heroic b4 but we dont have 2nd tank last week so we did spine on normal and turned heroic on dw.)it worked good last week but this week we couldnt do it again,thrall dont let us start heroic fight b4 all bosses dead on heroic,Anyone now any hotfix or blue post about it cus i didnt see any...
They must have hotfixed it.
I have personnally been in a group where we killed 6 heroic, then normal spine and then we just tried heroic madness and we were able to start the encounter. That is without even having the heroic spine achievement. That was a few weeks ago.