The Dead Do Not Forget...

It seems as if the skulls do not respawn properly at this point. I searched the area for some time looking for the last one, and none of the previous skulls came back. I still have not located the last one.

Grants the buff [spell=176798] upon completion. 5% xp buff from killing enemies for 1 hour that persists through death.

This quest is a PITA. You can easily be overrun by multiple mobs that stealth and popup out of nowhere. There are other mobs constantly pathing around. You will have to go into all the caves to get enough skulls. As noted, they do not respawn. Do not kill Boneseer Cold-Eye until the very end when you have all your skulls. You'll have to kill him to get to the cauldron to complete the quest. The quest doesn't seem to link, might be a good one to skip.