Victor Vran

This achievement is story related, and it obtained by defeating the boss Vail the Immortal who is located in the Mausoleum of Bones.

The fight is a bit annoying. Every time you kill Vail, he basically turns into a small cloud, and quickly retreats to his Phylactery (a vile that is in the middle of two sentinels.)

I used a lightning gun to hit him from afar in order to dodge his projectiles. After killing him, I would try to follow him, but stop when I thought there were too many skeleton enemies.

By the time I killed the skeletons, he would respawn, so I would kill him again, and progress a little further until I was finally able to reach the Phylactery. At that point, I focused on the two sentinels, then destroyed the vile, so that I could finally kill Vail.

There's no point in fighting this guy more than you need to, you CAN speed run it by running straight to the vial, grabbing the 2x damage next to it, and going to town on said vial, and then on Vail.

Or, take your time and kill the swarms of skeletons and skeleton mages as you progress (you'll have to fight about 5 or so large groups if you do it this way, but will probably fail less than speed running it).

I used a fairly powerful hammer and was able to kill most enemies in 1 or 2 hits.