High-level instances bugged
The Raids and Dungeons forumgoers are up in arms about major bugs in Tempest Keep's Mechanar and the Caverns of Time Black Morass event.
The Black Morass, also known as Opening the Dark Portal, features portals of angry dragons coming to stop Medivh from opening the Dark Portal. You have to kill these mobs to preserve the timeline. However, it looks like the spawns of the portals are either really random or really bugged. Sometimes multiple portals spawn at the same time, and sometimes you wait ten minutes and nothing spawns at all. Poptrix of Bloodhoof suggests that setting loot to free-for-all and looting everything off the corpses evens out the spawn times a bit.
Tempest Keep's Mechanar features an elevator that appears to have some issues being visible. Some people can see it and others can't. This bug killed a run of Mechanar for my guild a couple nights ago. Hortus on the Bug Report Forum says that Blizzard is working on it, but many people trying to get attuned for Karazhan are pretty upset that they can't progress in Mechanar. Kink of the infamous "PALS FOR LIFE" suggests a fix:
Leave a group of trash at the very back corner up.
Kill the boss, rez, and loot.
Have a rezzer who can see the elevator go up the elevator and stand at the top.
Pull the last trash group, using crowd control methods to make sure they don't leash, and die to them in line of sight of the rezzer.
Have the rezzer rez your group. Voila, you are now at the top of the elevator!
Durnk of Ropetown also suggests the Overrated fix, where you replace the elevator with some spiral stairs.
There have also been some reportedly bugged invincible trash mobs in the Botanica, but they're easily avoided. Have you run into any bugged instances lately?
