A few little tips for the final boss:
Tip #1 - to avoid Dark Mist, tanks should space themselves at max (or as close as they can get) melee range from the boss. This will give you the time needed to strafe out as soon as you see the red circle (quick fingers still helps a lot)
Tip #2 - you have a relatively long time to down adds, getting them to low health (15-20%) or using LB will force the boss to eat them. This is a crucial point for the second wave where 2 adds spawn because downing 1 quickly will force the boss to try and eat both, however, downing both to around 50% and then killing one will give you more time to kill the remaining add before she can eat it. This holds for the final add as well, where using LB will force her to eat it early meaning you should hold off using it at all during this phase if possible.
