Here's just a tip for the frozen dragon boss, Keristrasza, in Nexus. This should work for regular too but its probably not needed.
Okay, the real fight can be tricky, and unless you have good dispels you might have trouble. The other night, i discovered that the boss can be kited around her chamber. I did it with a BM hunter, using Nitro Boosts and Bestial Wrath. When/if you wipe, have someone who has some method of removing frost nova and gaining speed, run around the wall of the bosses room. The boss will occasionally freeze you, but if you stay far enough away you will remain out of her LoS. Then, because the graveyard is so close, have the rest of the group quickly run back in and continue the fight. Have the healer get the tank back to full, drink/eat if needed, and then let the tank get aggro before restarting. The boss will be at the same health that you left her, and this "kiting" method can hypothetically be used forever.
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This is tried and tested several times with a hunter, and I'm sure that it's possible with another class/ability. One thing to make sure of is that you kill all the dragonkin adds around the diamond. Hopefully you won't need this, but its a nice safety to have. Makes it possible even with a shit group.