Neon Abyss

As the description says, in a single run you need to buy every single item from four different shops (one per floor). This can be extremely difficult (mainly luck dependent) to do naturally. Thankfully, there is an exploit to take advantage of to basically guarantee this achievement.

What you'll want to do is start a new save file. From the main menu, select Save Slot and choose an empty one. This will throw you into the tutorial (remap the controls if need be). Proceed through the tutorial to the boss fight against George, God of Pills. What's important to realize is that during the tutorial, you can't die. You can get hurt down to half a heart, but then you're invincible. By now you've likely noticed that George continually spawns 3-4 flying enemies, and when you kill them, they tend to drop worms. Stepping on those worms releases at least one coin, but sometimes multiple. Since you can't die, what you're going to do is avoid shooting/killing George, and instead just keep killing the enemies he spawns, stepping on the worms they drop so you get coins. In a shop, there is always a weapon for 40 coins, an item for 70 coins, and two items for 30 coins each, meaning you need 170 coins per shop, so 680 coins total across all four shops. You can therefore farm enemies against George until you grind out at least 680 coins. It may sound tedious, but it actually doesn't take that long at all (20 minutes, maximum). To be safe, I recommend grinding out more. I went all the way up to 999 to be safe (that's the max you can have). Once you're done grinding coins, finish off George.

Here's the only tricky part: after beating George, you'll presumably still have only that half of a heart left at the start of the next level. Worse, and what's important to be aware of, is that even though the game says you've now on Floor 2 after beating George, the game considers it the first floor if you try to use the Save Reload Exploit. This basically means that, after grinding out that money, you now need to get through the next floor without accidentally dying. Assuming you're playing on Easy, this shouldn't prove too challenging. Just play it safe in combat rooms, and try to get to the first shop ASAP so you can buy either the heart or shield for sale there, plus the item and weapon to help survive.

Once you get through that first real (non-tutorial) floor (making sure to buy everything at that shop), the rest of the floors shouldn't be an issue. You can use the Save Reload Exploit whenever if need be, and since you have so much money, you shouldn't have any issues surviving and having good weapons and items. You'll obviously need to progress to the shop on the fifth floor, buying everything on the way, but as soon as you buy everything from the shop on the fifth floor, this achievement will unlock.