In Karazhan, when fighting Prince Malchezaar, if you fight from the tunnel with only the MT and melee DPS in the outside area you can avoid all the infernals.
Have the MT tanking him about 5-10 yards out of the door with his back to the rocks on the right.
Melee will still have to run in and out as usual.
Healers stand behind the door (inside the tunnel) out of LOS of the boss but within LOS of the MT so they can heal him/her. Note: You can heal through the door.
Ranged DPS just stand as far back in the tunnel as they can.
And you have tank and spank boss. No more random infernals landing on you at 5%.
Note: If a ranged DPS or healer pulls aggro he will reset. Make sure the MT has aggro at all times. However this is not so bad anymore as they fixed the leashing bug. If a few people die it is possible to reset him simply by running the MT back in the tunnel.