
Pet survivability is tied to your own character's Toughness stat, in a bid to avoid invulnerable super-minions. Examples are Thunderstorm monster affix, Mallet Lord’s arm attack, or Morlu meteors.The basic idea is to make pets "roughly as survivable" as players, according to designer John Yang. Drastically reduced damage to pets - Persistent AoEs for which the player is intended to move out of quickly or highly-telegraphed attacks for which the player is intended to avoid altogether.

Good example are Perdition’s volley attack or Agnidox’s fireballs.

To counter that, game designer John Yang posted an update on the Diablo 3 forums outlining some of the changes Blizzard is working on to address the issues. As it stands, pets get punished when the monsters you're facing unleash attacks that are easy to avoid for the player, but not so much for the pets, since you can't control them individually. Pets are mainly the speciality of the Witch Doctor class but other classes can spawn them as well based on their skills. Blizzard is on the case and is looking into ways to make them more viable against the new challenges.

One of the few aspects of Diablo 3 that didn't get much attention with all the recent patches and the introduction of new difficult arenas, like the Nephalem Rifts and the Greater Rifts, is player pets.
