This achievement is story-based and will be received upon completion of the game and ending the final (third) level. It is given to you as soon as the credits roll.

I won't give you a walkthrough of each level, as this game is randomly generated each time you play, but in short:

-Always throw consumables before eating them, unless you KNOW it's a healing item.
-Look up now and then, avoid the hands.
-Don't be afraid to eat your weapons. Running is safer.
-Consumables are NOT carried over between levels, throw any spares you have to learn their effects
-EAT THE SHOTGUN AS SOON AS YOU SEE IT
-ALWAYS GO FOR PERKS

If you want a longer explanation of the game, I would advise looking to the parent game, Golden Light, and reading a couple tutorials from there.

Hard to quantify this one, but not an achievement you should worry about.

In short: Keep killing enemies until this achievement pops up.
This requires you to kill a 'black rose' which is a pitch black creature which spawns randomly. It's fairly common and very likely to come up if you make a habit of chopping enemies to bits.
Not much else to say, really.
Just keep swinging.

While playing the game, you should keep an eye out for Drops of any kind,
As indicated by Question marks on the map-boards, following these up and finding the item will either reward you with a consumable item, a key, or a weapon. There are a variety of weapons and items, but I wont be going over them. You should keep your eyes peeled for one weapon in particular.
LOOK FOR THE SHOTGUN.
Once you see it, grab it as fast as possible. You will not get another chance.
As soon as you have it in your hands, hold down the F key to eat it.

Upon eating it, you will get the achievement.

It doesn't matter if you're low on weapons or health, or even have full health, eat the shotgun. I had to grind for two hours straight looking for that damn shotgun, as it never came up for me. You cannot waste time here, I really cannot stress that enough.

If you are having difficulty finding weapons: Upon any level start, one weapon will be next to the elevator, shown below. If it isn't leaning against the wall, it's probably on the floor.
There will also be a map with little Question Marks on it.
Hit the map with your weapon until it dies so it drops a handheld version. This *may* ♥♥♥♥ you over with increased Enemy aggression, BUT taking the level slow can mean less fights (Just don't take it TOO slow)

As for other ways to improve your chances, I have heard a rumour that on higher difficulties you are more likely to find better weapons, but this may be false as I did not personally find any difference in the drops I was getting.
However, for certain, you WILL get better chances on higher levels, such as the level just before finishing the game. I would suggest gently skipping past the first two levels and speeding to the third and then, once you have cleared that map of resources, allow yourself to be killed.
This worked for me, and it may work for you. I know for certain that constantly refreshing the same level over and over IS a valid way to find higher tier loot, but it is a slow and painful process.

Sometimes, rarely, you will spot a 'Memento'. There is one on every floor, however the difficulty finding these may mean you miss out on one here or there.
These are floating, bright white Photos which can be interacted with. Upon activating them, a 'perk screen' will pop up and you have to pick one. Sometimes they will be above you, or hidden in 'meat-holes', so be sure to keep looking up and under desks every now and then.

Some of these perks are detrimental, some are OP. That doesn't matter.
EVERY TIME YOU SEE THIS SCREEN, CHECK TO SEE IF THE PERK 'GOLDEN BRAIN' IS AVAILABLE.
If it isn't, grab whichever perks suits you.
if it is, get Golden Brain. Ignore the other perk
The Achievement will pop up then.

Memento's are rare and if you have searched every ? mark on the map, honestly at that point, dying and respawning is a good enough strategy to keep farming them.
This will also be incredibly likely, as the longer you spend in a level, the more likely the 'Thorn of Rose' will come after you.

Hopefully, this achievement guide has helped you. This game is only a Demo for the main game, Golden Light. If this game intrigued you, I would advise going there for more. Lord only knows this game scratches an itch many people did not ever know they had.
If there are more details you would like explained, or expanded on, I would be happy to go into more detail as when I played, I found myself begging for a guide such as this. This game took me two hours to beat, but that time could have been a LOT longer, if I had worse RNG. I got lucky finding the shotgun, your experience may not be so merciful.
If you genuinely feel as though your RNG will never give you mercy, uninstall and re-install the game, this probably does nothing, but I have heard a rumour that it refreshes your in-game Number Tables, *possibly* improving your luck. I aint gotta explain ♥♥♥♥.

If you hated the game because it was unfair, I feel you. Then again, that's Golden Light for ya
If you loved this game because it was unfair, more power to you. You will love the full game.