If you kill them before you regroup them, low down your atk dmg around 100k to 120k that will maintain alive mobs during your regroup them, remove gems, change legendary weapons to rare weapons, reroll it for CDR, use season theme: In-geom+Messerschmidt’s Reaver+Leoric Crown that will give you an insane CDR, with that it’s really easy get master dungeon.
Hope help you gl hf!!! 
