Maid of Sker

Good news! This ain't hard at all and it doesn't require you to have played warzone the last year!

I was scratching my head after my one attempt killing every enemy with only 94 headshots. There wasn't even 150 enemies either. But I learned a "Headshot" is either a ping sound you get when you hit the head of an enemy, or when you blow it off.
What were going for is the ping headshot, which you get from the fireball guys since there head is visible and they take multiple shots, AND the point of this guide, the final boss guy.

Now play The Long night, and play it as normal, mabey getting as many headshots as you can, but the goal is to get to the end. You don't have to go crazy on collecting ammo since we will get it all back here in a second.
PRO TIP: Save your revolver ammo. Collect the ammo when you see it, and just use the rifle or shotgun to plow your way to the end.

Once you reach the boss room, press pause and check your headshot count in stats. Then continue into the boss room.

Here's where words will start to make sense, having saved however much revolver ammo, unload all of it in the bosses head, you will hear 6 pings (headshots) if you didn't miss. Revolver being the weakest weapon, it will prolong the fight aka more headshots.
Take your shotgun out when his minions come and blow them away then continue shooting the bosses head.
When you did all you could, or if he dies, press start, RELOAD CHECKPOINT and it will put you back right before the fight with all the headshots carried over! Then proceed to repeat what you just did over again and after 1 or 2 reloads, depending on how many you got during the run, you should have 150.
P.S Make sure you have 151 headshots and not 150 as I almost ended it right on 150. What are the odds.
Achievement pops at the results screen and as a added bonus, I got the A* rank when I did this run. Assuming its all the headshots/kills. So if your still needing that do this run first and hopefully you can nab that rank for this challenge.
Hope this helps!

First of all, we're talking about "The Long Night" challenge here.

HOW TO GET HEADSHOTS

1. Go to Settings and disable aim assist. Aim assist does not want you to get headshots and will actively work against you in getting them.
2. Use a gun (revolver, shotgun, or rifle). The axe cannot get headshots.
3. Don't use to aim. The crosshairs on the HUD are much easier for getting headshots than sighting down the barrel.
4. When you're shooting at an unaware target, get the vertical level of the crosshairs set up first, then wait for the target to walk into them. Use for precise left-right control - that is, walk side-to-side, rather than changing your aim with .
5. Know your enemy. Each one has different characteristics.
- Basic enemies, aka bagheads, aka "bags": The vast majority of the time, each bag is 1 potential headshot, and a headshot is a kill. However, there are exceptions, as I will explain below.
- Divers: It's impossible to headshot these guys. Hitting them in the head does no damage, and is just a waste of time and ammo.
- Ghosts: One headshot is usually insufficient to kill them, but it can happen. You can usually get 2 headshots on each ghost, and I've gotten 3 a few times. I suppose that was from when it separated into two parts.
- Elisabeths: You can get headshots, the first one is insufficient to kill, and it is possible to get more than 1. I've gotten 3 at times.
- Henrys: Just like Elisabeths, you can get headshots, one is insufficient to kill, and it is possible to get more than 1.
- Abraham: You can get a lot of headshots on him.

WHAT COUNTS AS A HEADSHOT?

There are several clues that let you know whether or not you've gotten a headshot:
A. The enemy dies
B. The enemy's head disappears
C. You hear a crunchy splat
D. You hear a faint metallic clang
E. The HUD crosshairs change orientation and turn red
F. The headshots counter is incremented in the stats screen.

None of this is totally consistent. I've had headshots register in the stats when I got a kill but the head stayed on and I didn't get the splat or the clang. There have been times when I shot a bag square on his nose and nothing happened - I thought, WTF, how did I miss that? - so I shot him again, got all the other clues, and when I checked the stats, I had 2 headshots on that one bag. There have been times when I've heard the splat and saw the head disappear, but it didn't register as a headshot. (The axe will sometimes give you a splat and disappearing head, but it will never register in stats.) I don't believe you ever get B, C, or D with Elizabeths or Henrys, but I have seen the red crosshairs. (Also, with Elizabeths, I've seen blood appear on her headbag.) That's why you can't go by any one clue. In the end, for the purposes of this achievement, the only thing that matters is F, the stats menu. But, if you get all of A through E, you can pretty well be assured you'll get F ... usually.

GETTING 150 HEADSHOTS

The first level, which is the attic and second floor, have around 22 to 25 bags and 4 divers. That means you have more than 20 headshot opportunities. What I did to get 150 in the playthrough was to farm this level, playing it through and then using "Restart from Checkpoint" in the pause menu. All of the headshots you've accrued will remain in your stats when you do this. When I had about 95 headshots, I moved on. These weren't speedruns - I took my time to aim and only ran a little bit - but I still got over 3.5 headshots per minute this way.

I then went to the next level, which is the first floor. I cleared it all out except for one Elisabeth that I didn't feel like messing with. Next was the ground floor. The first part of that level always gets way out of control for me, so I sped through it. Once I passed through the duct and came out into the quieter area, I resumed methodically clearing the level. Again, I left an Elisabeth, who was in the chapel, not bothering anyone. I cleared out the basement completely. By the time I was back on the first floor, I had 147 headshots. I got 9 in the battle with Abraham and his minions. You do get the clang and red crosshairs with Abraham.