Skull of Greed
     obtained from Barraccon The Piper @ The Vermin Horde Champion Spawn (Difficulty: 2/5)

Skull of Power
     obtained from Rikktor @ The Cold Blood Champion Spawn (Difficulty: 1/5)

Skull of Venom
     obtained from Mephitis @ The Arachnid Champion Spawn (Difficulty: 3/5)

Skull of Death
     obtained from Neira the Necromancer @ The Unholy Terror Champion Spawn (Difficulty: 4/5)

Skull of Pain
     obtained from Semidar @ The Abyss Champion Spawn (Difficulty: 4/5)

Skull of Enlightenment
     obtained from Lord Oaks @ The Forest Lord Champion Spawn (Difficulty: 5/5)

Combining all skulls will allow the group to summon the Harrower. The skulls can be combined using an altar found in the Star Room, an area accesible via a pre-marked rune or a trek deep into Terathan Keep. By placing the skulls on the altar a gate will open and teleport players to the dungeon where the Harrower will be found.

See the link below for a more detailed guide on champion spawns.


- Article by Cynic