The Harrower is the first incarnation of the 'Super Champion' of the Felucca Dungeons. Not to be confused with the Tentacles of the Harrower from Khaldun, which is apparently only a small part of The True Harrower.
The Harrower will only spawn once all the other six champions have been killed and their skulls have been placed on the altar in the Star Room in Terathan Keep. Once the skulls have been placed, then The Harrower spawns in a random dungeon.
The Harrower's first incarnation will be a relatively small black robed figure, but despite its small size it is incredibly powerful and will take a long time to kill.
Once it is killed and you think it is all over... It's not! You are in fact not even half way through it yet. The killing of The Harrower will only lead to the appearance of its second incarnation, The True Harrower, which is a huge dark and many armed creature of immense power.
Killing The Harrower is no small feat but it can be very rewarding in the end, if you can also manage to kill it's true form, which might result in a stat power scroll.