When aggro'd these guys take their right hand and reach around behind themselves, and then hit you with that hand. Makes me wonder what they are doing back there, it is almost as if they are pulling something out of their butt.
Yes they do summon. And see invis. They also use various blind spells, AE and single. The small ones proc a mana drain... Annoying when you can only box an SK for tankage. Luckily, they dont hit hard, are slowable, so monk-boy can tank these easy. The small ones depop after a couple of minutes, so no big deal about those. The small ones are immune to slow...
For gate-necklace questers:
What i usually do is pull a path from zone-in to the gate, just wide enough to run through, have monk tank, zone Shaman out when mob is about 5% (remember, they heal, so be sure its oom first), FD the shadowknight. Monk can beat down the mob easily by himself. FD monk once the small ones pop, and just wait it out.
The two at the gate require some FD splitting, not too hard since they cast alot, so just keep flopping till you have 1 single, or take both if you want. Once those are dead, can move group up to gate and in. Just pull mobs to there, or go in. Whatever you prefer. The mephit model mobs are up the hall and to the left. Watch for roamers.
These guys are all over when you zone into PoA. Although they aren't directly at the zone in, they're extremely close by, so you don't have much room to wander around when you zone in.
When you kill them, they will split into several small pieces of armor, which look like miniature versions of the Castellans. These are called "A Vengeful Spirit" and are fairly low level (conned light blue to me at 65). I've seen them spawn anywhere from 1-4 "A Vengeful Spirit"s upon dying.
They also have the chance of spawning a named mob when they die ("Inlokher the Warlord" is one that comes to mind), so be alert when they die.