Collect 3 Lion Rings, via the Lion Ring Quest, and say Lion Rings, then yes to Mordenthal, located in his temple, in the Mountains North of Stonecrest.

Note: You must be of evil alignment to perform this quest!

Rewards:

• Armageddon Cloak or Raven's Great Axe
• Karma decrease karma

In total, 1 reward will cost you 1125 Moon Tug Scalps (i.e., 375 Moon Tug Scalps per Lion Ring)!

You can repeat this quest at will.