The Evil Within

At the end of chapter 10 you will encounter Laura, which is the weird creature with long hair and multiple limbs. You will need to kill it before running towards the elevator, if you go too far and the cut-scene shows you enter the elevator you will need to reload your last save.

It takes a ridiculous amount of damage before you can kill it. But you can cause a small amount of damage to it by shooting the valves on pipes so it walks into the flames or burning dead bodies when it walks over them. But even after using all of these that were available it didn't die.

So I replayed this chapter on New Game plus so I could use the rocket launcher that you unlock at the end of the game.

The bitch is back and this Achievement can be very tough. I attempted it for almost 3 hours with no luck on Easy and I had 4 Explosive Bolts, 2 Lightning Bolts, 4 Grenades and ALOT of Ammunition. I burnt every body and hit every valve and nothing killed her so like most I loaded it up on New Game and I would advise anyone going for it to save your sanity and do the same.
With the Rocket Launcher it doesn't take much to kill Laura. So still do the same things,

Light Bodies
Light Valves
Use the Explosives on her

Most importantly is a fact that I have discovered, related to the damage contribution to Laura, that actually counts towards her death. Damaging her, only is ultimately efficient during the final section of her scene. This is when you fall down: I burnt the three bodies located there when she spawned out of them, and once she appeared and was in flames, I hit her eight times by meele (only hit her seven times when you burn the last body, or you will die). I also shot the levers of the two pipes there, and hit her by hot fluids like that - again, I struck her with meele attacks (about three should be save to perform). The other lever there remaining, you can shoot at, can not be used to cause damage to Laura - very ridiculous! Instead, you must damage her by using your own stuff now. I used about ten Flamebolts (No meele during her being flamebolted, because this fire is flagged to cause damage to you too - what a mess!), until she was vanquished. Time to burn that demon of the mind!

Note, that this outcome can be only absolutely reliable, if Meele attack damage and Flamebolt damage are at their ultimate levels, and the game mode is at its lowest level.

Laura must die here to become able to get to some items, including a Goddess Statue for a Locker Key! If you do not kill her there, you will not have the possibility to turn right in front of the elevator there, because your escape will be automatic when exiting the last hallway there at.

Near the end of the chapter 10 you'll fight again against Laura. You'll have to finish her without escaping the area. The first time will be a bit difficult, but if you carry enough material to make bolts (especially fire bolts) it must not be that complicate. Youcan see how to do it in the video.

During the ending of Chapter 10 you will be chased by Laura. You will want to attempt the achievement on New Game Plus, where you have the rocket launcher. When you get to a room where you need to shoot pipes to continue is when you want to start damaging her. Get to the opposite side and freeze her with the freeze bolt, then whip out the rocket launcher and fire a shot into her. Be careful because the launcher has a long reload and you can't move when it is equipped, once Laura is unfrozen switch back to the crossbow quickly. After she take a lot of damage, she will leave. Now shoot the pipes and drop down to the next level. Continue to freeze and fire rockets into her. Also in this section you can use the fire traps as will.

I was able to do this achievement on my first playthrough on Survival mode, without flame bolts. It took several tries but its definitely possible. I did it twice. (see below) I think the key strategy is to use all the available flame traps and blow up the bombs near Laura as you approach the final checkpoint before the elevator. Save your ammo until after the checkpoint before the elevator.

In the last section before the elevator use shock bolts to stun Laura, preferably near bodies, then burn the body which should ignite Laura, then blast away with your best guns. I used the Sniper Rifle and Shotgun mostly, going for headshots, and even had ammo left after the fight. I also used explosive bolts as mines so Laura could walk over them. I didn't create new bolts during the fight since I was too low on parts. I probably used 3 shock bolts, 1 or 2 freeze bolts, 3 explosive bolts, and 4 harpoon bolts during the fight, as well as several shotgun, handgun, and sniper rounds.

After the fight I was able to get the items and Statue key near the elevator, which was my goal since I wanted the collectibles and key achievements on my first playthrough.

NOTE: The elevator section can be glitchy. I actually killed Laura twice. The first time I killed her the achievement popped, but the elevator did not appear where its supposed to so I was stuck. I went to the elevator shaft, jumped, and fell into a black abyss. Eventually I landed and walked around aimlessly for a few minutes in the dark, and restarted the last auto save since I wanted the statue key in my first playthrough. Another time Laura did not appear for the final fight near the elevator, so I tried to get the key but the cutscene prevented me so I restarted.

Much like the rest of this game, the secret to this achievement is turning on infinite ammo.
You can find infinite ammo at the bottom of the options menu.

When you come to the area late in the chapter when you see Laura trapped in a cage (she looks like Kayako from Ju-On mixed with Regan MacNeil from the Exorcist. First seen in Chapter 4) make sure you have infinite ammo turned on and an incendiary crossbow bolt crafted.

Once she escapes the cage after pulling the lever I would hit her with the incendiary bolt then switch to the double barrel shotgun and spam fire. She will eventually disappear.

Continue through the map doing this exact same thing every time she spawns and eventually you will come to an elevator. This is the point where she is technically killable so repeat the strategy of incendiary followed by spamfire double barreled and she should be dead in seconds.

Once she disappears into a pile of green goo (8000 no less!) scoop her up and continue on with the level.