Here, I will cover all the basic achievements that you can do before doing the obscure ones.

ᴛʀʏ ᴀɢᴀɪɴ
Die for the first time. If you want to get the rest of the deaths achievements, you can go to the save editing section to learn more about it.

ᎶᎬᎬᏃ, ᎪᏒᎬ ᎽᎾu sᎬᏒᎥᎾus?
Die on the first chapter. Simple enough but if you missed this achievement, you can go to the save editing section to learn more about it.

y̷o̷u̷ ̷t̷h̷i̷n̷k̷ ̷i̷t̷ ̷w̷i̷l̷l̷ ̷b̷e̷ ̷e̷a̷s̷i̷e̷r̷?
Connect the gamepad. I use the xbox 360 controller and it works.


🅃🄷🄰🄽🄺🅂
Make screenshot and attract more test subjects. Just press your screenshot button (Mine is F12) and the achievement will be yours.


ⓄⓃⒺ,ⓉⓌⓄ,ⓉⒽⓇⒺⒺ,ⒻⓄⓊⓇ,ⒻⒾⓋⒺ,૭૦૦ძ ც૦ע,ƧУƧ✞Ǝℳ ƎЯЯøЯ
Just complete the main game. Also, the roman number on "ⒻⓄⓊⓇ" achievement its actually number 6 and not 4 lol.

Thats it for the basic achievements. Now lets look at the obscure achievements.

I recommend you to finish the game first before doing this. Anyway, the first thing to do is to find your save file. Your save file location will be located on:
"C:\Users\<Username>\AppData\Roaming\MMFApplications".
You can use Windows key + R and search "%appdata%" to open your roaming folder faster.

Once inside the folder "MMFAPPlications", you should see a file name "Dead.File". Backup the file first for safety reason. Then open the file using notepad and you should see something like this:

As you can see, there should be two line of text.

The first line is "♥♥♥♥♥♥♥♥♥♥♥♥"
This is your death counter. Everytime you die, the counter will raise by 1. If you want to get the tedious achievements (I mean come on, Die 1000000 times for a very short game?), then you can edit the number by putting the values such as 99 for "ᴏɴᴇ ʜᴜɴᴅʀᴇᴅ", 999 for "ᴏɴᴇ ᴛʜᴏᴜsᴀɴᴅ", 99999 for "🄸🄳🄸🄾🅃 ☹" and 999999 for "𝕥𝕙𝕖 𝕓𝕚𝕘𝕘𝕖𝕤𝕥 𝕚𝕕𝕚𝕠𝕥 𝕚𝕟 𝕥𝕙𝕚𝕤 𝕨𝕠𝕣𝕝𝕕". I'm sorry dev but this is too tedious for me.


The second line is "DeadTimer666"
This is the level of the game. You can go to the previous level (such as level 1 if you haven't got the achievement "ᎶᎬᎬᏃ, ᎪᏒᎬ ᎽᎾu sᎬᏒᎥᎾus?" like me for dying at chapter 1) by setting the value from 1 to 49. If you change the value other than the given value (50 and above), you will get different results. This is what I get from my experiments.

ıllıllı 『Ⱨ₳₵₭ɆⱤ』 ıllıllı
For this achievement, we need to set the value either 64 or 67 and above. I use 100 like so:

and you will get something like this:
The game will give you the achievement and automatically close and it will be like this until you change the value back to default again (1 to 49).

If you set the value to 50-66 (except 64), you will get something like this:
There's a choice that you need to make, in this video, I choose yes but if you choose No, the game will be close and your save file will have another line of text call "NO=1". If you decide to launch the game next, you will be in a infinite loop. Just delete the line "NO=1" and you should be good to go.

Also, I should mention that when you see this screen:

You can actually press escape to go to the main menu and press play. Every value from 50 to 66 has its own outcome.

Here's the result from my testing:
Values : Description
50 = Credits.
51 = Ending of the game.
52 = Dead_File EXE title screen with text (This is the same as you didn't press esc on the screen that I mention)
53 = When you choose no.
54 = When you choose yes. (You can actually watch the video above to see from 52-54)
55 = You will get the achievement "ʏօʊ'ʀɛ ɨռ Ꮖɦɛ ɢǟʍɛ".

Here's a youtube video:
56 = Some russian text that I can't understand at all.
57 = Instant crash.
58 = Insert coin and Blue screen of death. (And it crashes the game)
59 = Instant exit the game.
60 = Black Screen.
61 = Instant exit the game.
62 = Public Level screen.
63 = Instant exit the game.
64 = This is the screen to get the ıllıllı 『Ⱨ₳₵₭ɆⱤ』 ıllıllı achievement.
65 = Some sort of level editor that you can't use.
66 = A playable level. I won't spoil it though, you have to try it for yourself.
67+ = Same as 64

If you have any question, let me know and I'll try to answer your question as best as I can.