This dungeon is designed for higher players mainly due to the power of bosses as they do high damage for a low amount of element charge. So i would recommend using a level 15 plus character to kill monsters.
Where To Access:
To get to Oblivion type /join solace and then find him and talk to him the press "nightmare dungeon"
Note: Red star is the starting point
Blue star is the boss point (Witchblade and Fiend of Vergil and Storm Knight)
Fiend of Vergil
Some characters are random
You may also encounter the Shadow Pikeman or Crypt Samurai