Here is a Nightmare House The Original Mod Guide Wiki and For player’s 100% Achievements it should be easy.
Nightmare House The Original Mod Guide Wiki – 100% Achievements
Campaign
1. Escape was Always an Option
Finish Nightmare House 1 (Prologue)
Difficulty: 2/5
Tips: Finish Chapters 1 to unlock
2. Escape was Always an Option
Love it or Leave it
Difficulty: 1/5
Tips: In Chapter 7, choose to leave the hospital (BAD END)
3. Clean Bill of Health
Face your fears and complete the game
Difficulty: 3/5
Tips: In Chapter 7, choose to press the elevator button and KILL Dr. Romero (GOOD END)
After visiting Dr. Romero’s base and getting down, go to the machine place. Start boss fights:
- First: Pull down the lever to disable the shield
- Second: Break the pillars (Wood)
Repeat the operation
4. One Fell Swoop
Kill multiple zombies with a single axe swing
Difficulty: 2/5
Tips: Watch it
5. Right in the Brain Box!
Blow off 10 zombie heads
Difficulty: 2/5
Tips: Crosshair (Hold E) to zombie’s head, then cut it off
6. Hot and Bothered
Light a Riot Guard on fire
Difficulty: 1/5
Tips: Use lighting sticks to light guard zombie (Not normal zombie!!!)
7. What were you expecting?
Return to Romero 3 times from the laundry room to break immersion
Difficulty: 1/5
Tips: Very easy nahnahnah
8. No, the other guy!
Shoot the SWAT Leader instead of the other guy
Difficulty: 1/5
Tips: Kill Leader
9. The Voice Behind the Slaughter
Meet The Announcer before leaving the hospital
Difficulty: 1/5
Tips: Follow
Special
10. Thrills, Chills, and Acro-Skills
Use upwards momentum to jump through the Elevator Hatch in Chapter 2
Difficulty: 2/5
Tips: Not hard, just catch timing
11. Here comes the BOOM!
Find the shotgun earlier than you should in Chapter 6
Difficulty: 2/5
Tips: At start, find 3 boxes stacked high under the green container
12. Let the bodies hit the floor
Knock over all mannequins in the dark room and find the secrets within
Difficulty: 1/5
Tips: Knock over all mannequins in dark room
13. The Deliverance of Dave
THIS IS SECRET
ATTENTION!!! You must unlock 12. (Let the bodies hit the floor)
If you don’t, you won’t be able to enter the secret level
Difficulty: ?/?
Tips: After 12. (Let the bodies hit the floor), a red hole will appear. GET IN AND JUMP IN. GO FINISH IT
14. Get Some A.S.S.
Experience NH’s Auto Scare System 10 times
Difficulty: 4/5 (FOR LUCK)
Tips: This may spend you lots of time. You had to know A.S.S (Auto Scare System) is a random system.
Yes, random. This is to test your luck.
I’m playing for 2 times to unlock it.
So I found A.S.S from wiki ↓
The Auto Scare System is a random system that happens in Nightmare House 2. The Auto Scare System happens very erratically to catch the Patient off guard. The scares that are produced by this system are slaps on the back of the head, which most likely come from Emily. The Patient will hear a “psst,” or their flashlight will start flickering, or the screen will be shrouded by static. The screen may also say “DON’T LOOK BEHIND YOU!” or “HELP ME!” Another scare that involves Emily will have her appear right behind the Patient, overshadowing them, and then she will disappear.