When to Kill Malthael?

Defying Death - Kill Malthael at the highest level, within 3 minutes, while playing at the Torment level, or higher, in the hardcore mode. You can turn on the mode only while creating a new character.

What type of damage does Malthael do?

Instantly teleport through an enemy afflicted by Reaper's Mark, dealing 59 damage and refreshing Reaper's Mark. Can only be activated if there is at least one enemy affected by Reaper's Mark. Malthael teleports to the opposite side of the target from his location at 1.5 distance.

How do you kill Malthael in torment 4?

Make sure never to stand in the clouds as they do unfair amounts of damage in a short time. Never attack him while he's in the middle. Basically just wait him out. You spent the whole fight avoiding him and trying not to die, and eventually, after about 20 min., he will finally die.