There is a run in the crystal caverns, which are beyond sumpter in rune, look of mark of dawn or dusk to find out how to get the crystal caverns. There is cpk and the mob is cpk so be careful. when you find a mob that absolutely will not let you pass, its the same area as like a pinch of salt or something??? then you are in the right area. Have a friend die and either run to your area or summon shade should work, you need to be dead in order to get past the guard, there will be a lever or something that the dead person needs to pull which will cause a nexus to happen in the room past the guard, the portal leads like 1 room away from the guard on the other side, so the alive party has to walk i think its east or southeast and enter the portal which will take them north of the guard. to the north of that room is a mob that you need to kill. As far as i can remember he is not easy. I believe you need acid weapon to do damage, and be wearing some kind of metal i think its all copper if i remember correctly.
I recommend 2 stout archons or more, death is not that big of a deal you can easily get back into the room.
The loot is limited to only 1 of the mage classes. Not going to tell you if its worth it until someone does the run or someone else ruins the surprise.
Good luck