In the Lair of Terris Thule: Hits for a max ~6,500 and has ~10 million hitpoints; spawns numerous butterfly adds at 75% and 65%. Her AE dispell is cast at 50%. The gargoyles surrounding the lair activate at 35%.
In the Plane of Time: Hits for a maz ~10,500; single-target rampages; spawns four adds every 20% health (for more information about how the event works, see this quest entry).