When you're doing the beginning of Karazhan, and get to the pulls after Maiden of Virtue, you have 2 double pulls of the mobs that do Ice Tomb on your tanks. There's 3 ways to get around this causing a wipe.
Firstly, is the very obvious crowdcontrol on one with Shackle Undead, and then use 2 tanks for the remaining mob. (everyone knows this one.)
Second option is to have 2 tanks yet again, but use a Shaman in the tanks' party to lay grounding totem. So both tanks build aggro on both mobs (since you dont have shackle for CC**), and the grounding totem then absorbs the Ice Tomb from one tank, thus allowing both to aggro onto the backup tank.
The Final option that I have found is for those groups with only one tank. You need 2 shamans, and the tank all in the same room. Both shamans lay grounding totems, thus absorbing both Ice Tombs, allowing one tank to easily tank 2 of the mobs.
Pretty much, for options 2 and 3, the shamans just relay grounding totem every time they can, and I've only ever seen it absorb Ice Tomb (not the frost shocks).
Also. sorry for not knowing the names of the mobs off the top of my head, the Ice Tomb is a dead giveaway of who im talking about though. (If anyone knows the name, post please.)