Undying Rage

Undying Rage is a Defensive skill used by  in Diablo IV, working similarly to Nerves of Steel.

In-game
Undying Rage is a passive effect similar to those found in the previous game. Upon dying, it gives a small window of time to kill any enemy (not necessarily the one who actually delivered the killing blow to the Barbarian). If successful, the character's death is undone. Can only happen once every 2.9 minutes.

While under this effect, the Barbarian is reduced to 0 Life, and will not take any further damage, but can still be affected by Crowd Control.

Additional Ranks increase the amount of healing and reduce the cooldown, but do not prolong the window.

Trivia

 * The mechanic seems to be copied from Warswords of the Valarjar in World of Warcraft.