I decided to finally make an achievement guide for this game. I'll make a video for all of them, and add a link to it in the comments.

Boring ones

LOG INNN!!!!!!!: Just log in into your GameJolt account.
¿You know what you're doing, don't you?: complete a night without doing anything, only possible in custom night.
Gumball: with a slim chance, after lowering your monitor, you can see a gumball.
JUST DIE!!: just die

Main ones

The first night: complete the first night
To slow my friend: complete night 2
Two more: complete night 3
Harder, Nah!: complete night 4
Information obtained!: complete night 5
Consumed by fire..: complete night 6, although it's insanely hard
¡With family again!: complete all 4 minigames

Fun achievements

1984/12/06: set all animatronics on a respective difficulty

Hard achievements

I'm a professional survivor!: survive 20 minutes in survival mode
No one can stop me!: beat 9 preset challenges in custom night.

Insane achievements

..Real ending..: complete 8/10 mode(THE END preset). Better don't even try it. It's insanely RNG based...

I'll do PJ 2 and FNaJ 4 VS achievements guides coming soon. Real soon.