Karazhan Trashmobs Tactic

A short tactical explanation.

So, while much of the trash in Karazhan is somewhat straightforward, there are some notable exceptions.

Skeletal Ushers
Found alone, or in pairs of two, these are amongst the more annoying critters that inhabit the tower. They are immune to all forms of crowdcontrol, as well as taunt.
Apart from hitting like a truck, their most dangerous ability is to cast a frost-trap-like effect on the person tanking them. Since this effect occurs fairly often, and also quite early in the fight, they require at least two tanks to be dealt with, and for the pairs, preferably three!

Both tanks must build aggro on all ushers in the fight. But since it is quite likely both tanks will get frozen, a third tank (a druid in bearform swiping, or a paladin casting consecration) should also build aggro on both. Important: the freezing effect also reduces threat by a lot!

Fortunately they die fairly fast, but keeping a tank with two of these on him alive is a daunting task for the healers indeed.

There is one important trick: while paladins Blessing of Freedom doesn't work on the ice-blocks, Potions of Free Action *do* work. Drinking one when pulling gives the tanks much more time to build aggro. Important: while the potion prevents being frozen for 30 seconds or so, the threat reduction WILL occur anyway.

EDIT: These mobs are shackleable and the Ice blocks can be remedied by the Grounding Totem.

Ghostly Philanthropist
There are a handful of these just beyond the Theatre-event. They despawn after a soft reset when the Theatre is cleared.
They are no threat. They do not hit hard. But no matter HOW tired you are after the Theatre-event, thou shalt go on and kill them all before logging, for they drop loads of gold each!

Arcane Watchman
Found near the Curator in pairs of two, these huge machines hit fairly hard and inflict a debuff on victims called OVERLOAD. When afflicted, the victims must move away from the rest of the raid because they will pulse with a damaging AOE for the duration of the debuff. Hence, the Watchmen must always be tanked far apart from each other.