To find this monster, from the entrance, go up to level 2 and then go up to level 3. On level 3, do NOT go down the hallway. Instead, go up to climbable wall right next to you to level 4. On level 4 you should be facing a small room that usually has a big metal snake in it. Either way, proceed into this room and go up to level 5.
Blacktalon vanquishers have quite a bit more health than most trash mobs of the same level - be careful when pulling.