Blizzard has shared the details on hotfixes that came with Patch 2.1.1Diablo 3.
First off, they outlined a hotfix for Thunderstorm, a boss ability. This is an Elite affix that allows bosses to hit a targeted area with lightning strikes over and over again. While this ability causes low damage, it can be annoying to ranged attackers, since it can strike them even if they are some distance away from the boss.
Thunderstorm was broken when it came to pets. The patch initially lowered the damage pets would receive, but because of the change, the affix would target the pets over and over again. This hotfix corrects that mistake.
The Realm of Trials was also modified by the latest patch. This area is intended to test your abilities, and determine what level Greater Rift you should be attacking.
They adjusted how monsters spawned in the Realm of Trials by reclassifying monsters into pools. Each pool would have categories for monsters that die quickly, that deal consistent damage, etc. Monsters that run frequently are removed from the pools, and the monster spawns provide a better experience overall.
They also reduced the Keystone tiers for multiplayer groups, but recognized that they overshot the counterbalance. In multiplayer, different players can share enhancements, and having a diversity of abilities also makes them more powerful. Blizzard will provide another future hotfix to address this issue.
