Magma Barrier + Life Regen

Unique enemies with magma barrier and life regen are just ridiculous to kill. The 5 second window of opportunity to deal damage is just immediately healed back even at level 30. If the enemy in question has armour it is nigh impossible to kill as to break their armour takes a greater period of time than allowed. Spent 25 minutes, used 9x4 health flasks and every skill possible to finally beat it for mediocre gear, feels incredibly unfair/bugged. Have lost a run to one previously.