Dead Cells

Here’s how I got the achievement…

When you enter the new Bank biome go to one of the ATMs and take out the max $20,000 debt. When you exit the bank biome the game will want you to pay $20,000 to open a door. Don’t do that. Instead, break the door down and you’ll get a “100 enemy curse”. CodeMonkeysGuy said that you can kill the 100 enemies to get rid of your curse and beat the game and you’ll still get the achievement. You don’t have to keep the curse till the end of the game.

You can use the dashboard-save-glitch so in case you die while cursed you can spawn back to whenever you dashboard-saved last.

Well, this guide is based on a comment by KlumpyPoo on the other solution:

This can be done on any BC but of course is recommended on the lowest one to be sure (0 BC).
This will be a series of suggestions to pass the 100 enemies curse.

When the game start and you have to choose the 5 items sets, try to pick these, in order:
- Serenade (because it will go and kill anything around, pretty useful for a curse like this, just avoid to activate if there is an elite enemy around)
- Leghugger (it will go and lick enemies on the same floor)
- Mushroom Boi (it will go and push any enemy on the same floor and, you can make him explode pressing again the skill button assigned)
- War Owl (it will attack enemies on sight)

If you choose to play the game on 3BC or higher, there is a small chance that the necklace at the beginning have the ability to make you invisible after 5 seconds of not attacking. This is pretty useful if you have Leghugger, Mushroom Boi or the War Owl, since they attack without you actioning, so you will keep invisible and undetected. It won't matter if you use stairs or change floors. If you have patience, almost all enemies can be killed this way.

The idea is to get the better stuff upon the bank entrance. The idea is to have it after the first level, and better pick "Toxic Sewers", which will be the level replaced by The Bank. If this not happen, restart the run and retry until appears when we want. I picked "Toxic Sewers" because after it you can travel to two more levels before a boss. Exiting The Bank replaced by it you choose "Corrupted Prison" (which has a little less than 60 enemies), and then "Ramparts" or "Ancient Sewers" (any of both have around 80 enemies. It will be up to you which level to choose.

So you went to "The Bank", level replacing "Toxic Sewers". At the beginning of the level borrow the maximum cash (20.000) and continue. The exit from the bank should be usually after the 2nd key you grab at the end of a floor. And break the door with your weapons. You will have now a curse of 100. 10 times the usual. Making you very vulnerable. Go back to the level and travel to the next two door. One will be the key and the other a door that opens with money (usually 2300). Since the level was replacing "Toxic Sewers" your most feared enemy will be the Scorpions, since they come up from the ground unexpected (unless you explorer almost all of the map). My suggestion is that each time you put the feet on a new floor, jump over a ladder, to avoid potential stings.
If you do this way, with the help of Serenade or some other companions and be cautious and
kill half of the enemies of the level you will later exit "The Bank" with a curse of 50 more or less. As suggested, avoid the scorpions and elite enemies. Beware with Serenate that tries to kill anything near.
After exiting the level with still a big curse, pick "Corrupted Prison". It has a Cursed Chest at the beginning that will ad you 10 enemies more to your number (you can avoid it). Beware of the Slammers and mostly the Toxic Miasma. If you manage to do as expected probably before the end of the level you will be lifting the curse. And now, the next part, you have to finish and WIN the game. You have to defeat HoTK or The Queen. The achievement will be unlocked when the credits roll.

Of course, if you want to make the things more easier, you can play with the accessibility options or use the dashboard trick. This guide is trying to get you the best conditions to achieve it.
I was able to do it using Serenade and Mushroom boy, and took me about 4-5 tries.