This is a two-phase fight. To begin it, have someone use the Grimoire when standing on/near the altar. This will cause a "Soulgrinder" object to spawn on the altar. During the first phase, non-elite L70 ghosts will occasionally spawn and move towards the altar, attacking the Soulgrinder. You have to kill them to keep them from destroying it; after about 2 minutes the first phase will end and Skulloc will spawn. You can track your progress somewhat by watching the pylons near Skulloc; one will light up about every 30 seconds, then he will spawn once all four are lit. You should attempt to conserve mana during this portion of the fight; also, because it takes a while, you can use potions early on and have them available again for Skulloc himself. (Note: during the first phase ONLY, anyone with a Grimoire and standing near the altar can right-click it to fear all the currently spawned ghosts for about 10-15 seconds. While this can help if you are overwhelmed, it also makes it hard to actually kill them. Chain fears may trigger DR.)
Once Skulloc spawns, he will move towards the group and attack. He has three primary abilities. First, he occasionally spawns groups of the same ghosts you fought in the first wave. The Grimoire no longer fears them, so you must actually kill, CC, or offtank them. Second, he will occasionally banish a group member for about 10 seconds (he did not seem to use this on the tank). Third, he will occasionally cast Corruption on various group members. This should be dispelled ASAP, as the damage adds up. Skulloc does not deal a tremendous amount of damage himself, although if your DPS is not extremely high, the adds can start to become a problem. Undergeared groups may want to bring additional help.
- The "Skulloc's Soul" object you must loot tends to spawn a bit above his body; if Skulloc is in an awkward position when he dies, you may not be able to loot it. If this happens, you can simply restart the event by going up to the atlar and using the Grimoire again. You probably want to drag him down near the altar, or up where he initially spawns, rather than on the hillside.