The petitioner on thins one is Seeq called Aekom. You'll find him nearby the entrance to Lhusu Mines in Bhujerba.
About 5 500 HP
Resistant to Libra
Nidhogg can be found in Lhusu Mines. He doesn't have any special attack and bases mainly on the brute force. His attacks are: Saber - very strong attack which harms also the user and the Tail Spear - a very strong attack aimed against one enemy. Nidhogg can also create strong and fast combos from ordinary attacks. What else can I say - hit him as many times as you can and look out for tank's HP level.
Bounty: 600 gil, Rose Corsage, Balaclava, Great Serpent Skin (70g).