WRT mobs summoning minions...
I remember one of those that was very brutal. In one of the Horde quest chains you have to kill a son of Cenarius, a level 28 named with two level 27 guards. Easy enough, right? Well, as it turns out, the named has a tendency to summon around a zillion treants the moment he notices you're there. We wiped several times against that joker. I only saw him beaten twice. The first was because our tank fell off the balcony, so we followed, and when the named chased us down I suppose he forgot to cast the spell. :) The second time was because we barraged him with Earth Shocks and stuns and managed to drag him down before he completed the spell. Hey, noone ever said that KotG were durable.