To kill Fergandir you will need a weapon with Westernesse or Belariand damage. When you pull him, any nearby adds will aggro to you regardless of your level. It takes at least two people to kill him.

Fergandir is one of the six named needed for the "Executioner of the Wicked" deed in Haudh Iarchith.

Here is a map for the rest of the "Executioner of The Wicked" deed