We already know that the Butcher sets the whole room on fire if you fail to kill him in 3 minutes.
Are just the end-of-act bosses that possess an enrage timer?
What are their effects? Is the timing the same for every one of them? Does the timer depend on the group size?
Best Answer
Since patch 1.0.4 Elite packs no longer enrage, and all boss enrage timers only take effect on inferno difficulty.
Boss Enrage Timers
Boss enrage timers appear to be specific for Inferno difficulty only
The Butcher - will set fire to all of the platforms in his chamber simultaneously if you fail to kill him within three minutes.
Ghom - will begin spawning 'Gas Clouds' more frequently after four minutes.
Zoltun Kulle - will enrage, using his 'Ceiling Collapse' ability more frequently, and for more damage after three minutes.
Belial - Enrages after three minutes in phase 3, increasing the number of green pools spawned, which will be spawned across the entire platform.
Cydaea - will enrage after four minutes, causing spiderlings to spawn more frequently.
Rakanoth - will become more aggressive after three minutes.