Neon Abyss

This is by far the hardest achievement in the game. Just as hard as this achievement is actually unlocking Abyssal difficulty. Refer to The Real Game (50G) for doing so.

Despite what you may read online in various sources, as of the writing of this guide in February 2023 (and presumably after all updates to the game have finished), once you unlock Abyssal difficulty in the bar, it's unlocked permanently, and there are no consequences for dying on Abyssal difficulty (there are no dots above the difficulty or anything like that to worry about).

*IMPORTANT* In my opinion, the absolute most important thing to know about your Abyssal run to beat Athena is that you need to be sure you don't go up against Cursed Zeus or Cursed Athena, as they're insanely challenging, and Cursed Zeus's level is so unfair you'll likely rage quit. So, to make this run as easy as possible (relatively), you need to be absolutely certain you do NOT meet the criteria to fight the Cursed version of these two bosses.
 

• For Zeus, this is relatively easy, as you'll need to raise your Wisdom to get an Athena Token anyway to even reach Athena for this achievement. Just make sure you have some of your Faith meter full when you go into the fight against Hal on the sixth floor. This will ensure that you get the regular Zeus level and fight the regular version of him. (If you beat Hal with no Faith, you run the risk of entering the Cursed Zeus level, which is essentially a run ender)
• For the Athena fight, you fight the Cursed version of her by filling your Wisdom meter on her floor (the eighth floor) and then teleporting to the secret room where you'd normally get to choose an item. Do NOT do this, obviously. It may seem like an unlikely thing to do on an Abyssal run, but it happened to me, and I didn't know what was coming. So, on the eighth and final floor, proceed to the boss door like normal. Do NOT teleport to an Athena room, if you unlock one.

As for the run itself, you'll obviously need to make sure you fill your Wisdom meter and get an Athena Token. All the good weapons and items don't matter if you don't even get the token to reach Athena. Like always, you're at the mercy of RNG to hope you get the token, as well as good items and weapons, but here are a bunch of tips to make it easier on you:
 

• Before even attempting this, unlock all of the skills in the skill tree at the bar that add items to the shop and add breakables to the rooms (heart barrels, shield barrels, key barrels, orange painted blocks, etc.), as well as the switches that open up secret rooms (one for no damage and one for full health). These are extremely useful, both for getting more consumables (grenades, keys, crystals, money), and for finding more hearts/shields to keep you flush.
• Character selection isn't a huge deal. I played as Ming, but you could just as easily play as Anna since she starts with four hearts.
• Obviously plan to use the Save Reload Exploit continually throughout your run if you do poorly on a floor, and especially if you're close to dying. I always did it when I was two hits from dying, just so I wouldn't accidentally die and lose that entire run
• You will likely have your own weapon preferences by the time you're attempting this, but my top weapons were always Animosity, Soul Bringer, and Meteor. My favorite was Animosity for the first six floors of the run. The angry sprites can go through walls, do a lot of damage to enemies (killing most normal ones outright), and they recharge very quickly. The active skill is also extremely useful - you can spend 5 crystals and 50 coins to upgrade your weapon. NOTE THAT LEVEL 8 IS THE MAX. If you reach Level 8 (very reasonable in a full run with the Animosity), don't waste any more money on upgrades, and don't even bother entering challenge rooms. One important thing to note about Animosity though, is that the angry spites are completely useless against Hal and against Athena. For some reason, they don't track and attack properly. Hal isn't bad to defeat with your regular shots from the gun, but Athena would be incredibly difficult with Animosity. I used the gun to reach Level 8, and then bought a new gun between floors six, seven, and eight, since gun level carries over to all weapons
• For items, especially when you have two to choose from, google every item before you pick one up. This is extremely important, so you always ensure you're making the optimal selection for your build and playstyle. While there are no "bad" items, there are some that can really mess you up, such as the one that drops a mine every time you jump. That mine can hurt you, making it really easy to accidentally hurt yourself throughout the run. Just google "Neon Abyss [item name]" to get a description of it on the Neon Abyss wiki. It's quick to do and can make a huge diffierence on your run, having the right items
• It should go without saying, but flying (Divinity or Pegasus) are probably the best items in the game. They make you so much less likely to take damage, clearing rooms is far easier, and the boss fights are so much easier to manage. Make these items top priority
• If you don't have Animosity to upgrade your gun, I highly recommend making it a point to complete the challenge room on each floor without getting hit so you get the gun upgrade. Athena is a challenging boss already, but having anything less than a top level gun will make the fight drag out even longer. I used the Save Reload Exploit for each floor until I beat each challenge without taking damage (or at least got the gun upgrade as a reward, which you can still sometimes get even with getting hit once)
• Use the Save Reload Exploit to optimize each floor. You don't want to go on to the next floor knowing you took multiple avoidable hits throughout combat rooms. If you get hit a lot and know you could've avoided it, retry the floor. Everything stays the same, so you'll be able to get better and be more efficient
• Leave all hearts and shields that drop from breakables and enemies until AFTER you beat the boss of the floor. You can pick up hearts to refill anything you've lost along the way, but NEVER pick up shields as you progress through rooms. The reason you never want to pick up shields as you progress is because if you take damage and lose a heart, you can replenish it with another heart drop. If you take damage and have a shield to lose, and your hearts are full, now all heart drops throughout a floor are useless. So, progress using only your hearts, not picking up any shields, so that heart drops can still be utilized if you take damage. Do this even for the boss fights, waiting until after you beat the boss to then go back through every room and pick up all the hearts and shields you left behind. Also stop back at the store and buy any hearts or shields there to refill whatever you need. NOTE though that you CANNOT go back once you enter the boss fights against Argus, Hal, and Zeus on floors five, six, and seven, respectively. You therefore should pick up all the drops BEFORE entering those boss fights
• Along the same lines as the above, after you clear all the rooms and after beating the boss on the first four floors (but before beating the boss on the fifth floor and above), go back through EVERY room. Even if nothing shows on your map, go back through every room. Make sure you didn't miss any pickups. If nothing is on your map, there still might be orange painted blocks to explode, barrels or jars to break that can drop stuff, etc. Also be sure to teleport to any secret rooms, as any drops in those rooms never show on your map. Check EVERYWHERE before moving on

Lastly, and this will be the hardest to hear, but sometimes you just need to give up. Even with all the tips above, you're still entirely at the mercy of RNG for your weapon and items. Some runs things just won't line up. There's no point in trying to force your way through bosses and floors with a bad weapon, even if it's leveled up, and with items that do you no good. I went into the Athena boss fight with 7 or 8 hearts, a couple shields, a Level 8 Meteor, the ability to fly, many pets, and good items, and it still took me 5-10 tries to beat her without dying. Trying to do so with a crappy weapon and useless items will make things way harder than they need to be.

Along the same lines, boss fights can't just be tanked anymore, nor can they be rushed through with powerful weapons. You will actually need to learn enemy attack patterns and get good at dodging them, Athena especially. After beating each boss, decide if you did well enough to move on to the next floor, or if you barely made it and should restart the floor. You shouldn't be moving on to the next floor if you only have one or two hearts left, as that'll make the next floor incredibly difficult to get a successful run. It may be hard to commit to retrying a floor after finally managing it, but it's better than a full restart of a run.

On my successful run (which you're about to see had a ton of good RNG in it), I got the Animosity on the second floor, and fully upgraded it by the sixth floor (thanks to early challenge rooms and then its active ability). I got Pegasus on the third floor, Hacking Tool on the fourth floor, and a bunch of other good items. On the final floor, I got a Meteor at the shop to buy and switch to, now that I was at Level 8. As I mentioned above, even with all those advantages it was still a tough fight. I restarted floors many times over the course of a few hours to make sure I progressed as safely as possible, and I still had to restart the Athena floor because of failing at the boss fight over five times. My point is that even with really good RNG, you're still going to need to "get good" to an extent, learning enemy and boss attack patterns to get through as much as possible without getting hit.

Once you beat Athena, the achievement will unlock immediately, and you can breathe easy know the hardest is behind you.

This is by far the hardest achievement in the game. Just as hard as this achievement is actually unlocking Abyssal difficulty. Refer to The Real Game (50G) for doing so.

Despite what you may read online in various sources, as of the writing of this guide in February 2023 (and presumably after all updates to the game have finished), once you unlock Abyssal difficulty in the bar, it's unlocked permanently, and there are no consequences for dying on Abyssal difficulty (there are no dots above the difficulty or anything like that to worry about).

*IMPORTANT* In my opinion, the absolute most important thing to know about your Abyssal run to beat Athena is that you need to be sure you don't go up against Cursed Zeus or Cursed Athena, as they're insanely challenging, and Cursed Zeus's level is so unfair you'll likely rage quit. So, to make this run as easy as possible (relatively), you need to be absolutely certain you do NOT meet the criteria to fight the Cursed version of these two bosses.
 

• For Zeus, this is relatively easy, as you'll need to raise your Wisdom to get an Athena Token anyway to even reach Athena for this achievement. Just make sure you have some of your Faith meter full when you go into the fight against Hal on the sixth floor. This will ensure that you get the regular Zeus level and fight the regular version of him. (If you beat Hal with no Faith, you run the risk of entering the Cursed Zeus level, which is essentially a run ender)
• For the Athena fight, you fight the Cursed version of her by filling your Wisdom meter on her floor (the eighth floor) and then teleporting to the secret room where you'd normally get to choose an item. Do NOT do this, obviously. It may seem like an unlikely thing to do on an Abyssal run, but it happened to me, and I didn't know what was coming. So, on the eighth and final floor, proceed to the boss door like normal. Do NOT teleport to an Athena room, if you unlock one.

As for the run itself, you'll obviously need to make sure you fill your Wisdom meter and get an Athena Token. All the good weapons and items don't matter if you don't even get the token to reach Athena. Like always, you're at the mercy of RNG to hope you get the token, as well as good items and weapons, but here are a bunch of tips to make it easier on you:
 

• Before even attempting this, unlock all of the skills in the skill tree at the bar that add items to the shop and add breakables to the rooms (heart barrels, shield barrels, key barrels, orange painted blocks, etc.), as well as the switches that open up secret rooms (one for no damage and one for full health). These are extremely useful, both for getting more consumables (grenades, keys, crystals, money), and for finding more hearts/shields to keep you flush.
• Character selection isn't a huge deal. I played as Ming, but you could just as easily play as Anna since she starts with four hearts.
• Obviously plan to use the Save Reload Exploit continually throughout your run if you do poorly on a floor, and especially if you're close to dying. I always did it when I was two hits from dying, just so I wouldn't accidentally die and lose that entire run
• You will likely have your own weapon preferences by the time you're attempting this, but my top weapons were always Animosity, Soul Bringer, and Meteor. My favorite was Animosity for the first six floors of the run. The angry sprites can go through walls, do a lot of damage to enemies (killing most normal ones outright), and they recharge very quickly. The active skill is also extremely useful - you can spend 5 crystals and 50 coins to upgrade your weapon. NOTE THAT LEVEL 8 IS THE MAX. If you reach Level 8 (very reasonable in a full run with the Animosity), don't waste any more money on upgrades, and don't even bother entering challenge rooms. One important thing to note about Animosity though, is that the angry spites are completely useless against Hal and against Athena. For some reason, they don't track and attack properly. Hal isn't bad to defeat with your regular shots from the gun, but Athena would be incredibly difficult with Animosity. I used the gun to reach Level 8, and then bought a new gun between floors six, seven, and eight, since gun level carries over to all weapons
• For items, especially when you have two to choose from, google every item before you pick one up. This is extremely important, so you always ensure you're making the optimal selection for your build and playstyle. While there are no "bad" items, there are some that can really mess you up, such as the one that drops a mine every time you jump. That mine can hurt you, making it really easy to accidentally hurt yourself throughout the run. Just google "Neon Abyss [item name]" to get a description of it on the Neon Abyss wiki. It's quick to do and can make a huge diffierence on your run, having the right items
• It should go without saying, but flying (Divinity or Pegasus) are probably the best items in the game. They make you so much less likely to take damage, clearing rooms is far easier, and the boss fights are so much easier to manage. Make these items top priority
• If you don't have Animosity to upgrade your gun, I highly recommend making it a point to complete the challenge room on each floor without getting hit so you get the gun upgrade. Athena is a challenging boss already, but having anything less than a top level gun will make the fight drag out even longer. I used the Save Reload Exploit for each floor until I beat each challenge without taking damage (or at least got the gun upgrade as a reward, which you can still sometimes get even with getting hit once)
• Use the Save Reload Exploit to optimize each floor. You don't want to go on to the next floor knowing you took multiple avoidable hits throughout combat rooms. If you get hit a lot and know you could've avoided it, retry the floor. Everything stays the same, so you'll be able to get better and be more efficient
• Leave all hearts and shields that drop from breakables and enemies until AFTER you beat the boss of the floor. You can pick up hearts to refill anything you've lost along the way, but NEVER pick up shields as you progress through rooms. The reason you never want to pick up shields as you progress is because if you take damage and lose a heart, you can replenish it with another heart drop. If you take damage and have a shield to lose, and your hearts are full, now all heart drops throughout a floor are useless. So, progress using only your hearts, not picking up any shields, so that heart drops can still be utilized if you take damage. Do this even for the boss fights, waiting until after you beat the boss to then go back through every room and pick up all the hearts and shields you left behind. Also stop back at the store and buy any hearts or shields there to refill whatever you need. NOTE though that you CANNOT go back once you enter the boss fights against Argus, Hal, and Zeus on floors five, six, and seven, respectively. You therefore should pick up all the drops BEFORE entering those boss fights
• Along the same lines as the above, after you clear all the rooms and after beating the boss on the first four floors (but before beating the boss on the fifth floor and above), go back through EVERY room. Even if nothing shows on your map, go back through every room. Make sure you didn't miss any pickups. If nothing is on your map, there still might be orange painted blocks to explode, barrels or jars to break that can drop stuff, etc. Also be sure to teleport to any secret rooms, as any drops in those rooms never show on your map. Check EVERYWHERE before moving on

Lastly, and this will be the hardest to hear, but sometimes you just need to give up. Even with all the tips above, you're still entirely at the mercy of RNG for your weapon and items. Some runs things just won't line up. There's no point in trying to force your way through bosses and floors with a bad weapon, even if it's leveled up, and with items that do you no good. I went into the Athena boss fight with 7 or 8 hearts, a couple shields, a Level 8 Meteor, the ability to fly, many pets, and good items, and it still took me 5-10 tries to beat her without dying. Trying to do so with a crappy weapon and useless items will make things way harder than they need to be.

Along the same lines, boss fights can't just be tanked anymore, nor can they be rushed through with powerful weapons. You will actually need to learn enemy attack patterns and get good at dodging them, Athena especially. After beating each boss, decide if you did well enough to move on to the next floor, or if you barely made it and should restart the floor. You shouldn't be moving on to the next floor if you only have one or two hearts left, as that'll make the next floor incredibly difficult to get a successful run. It may be hard to commit to retrying a floor after finally managing it, but it's better than a full restart of a run.

On my successful run (which you're about to see had a ton of good RNG in it), I got the Animosity on the second floor, and fully upgraded it by the sixth floor (thanks to early challenge rooms and then its active ability). I got Pegasus on the third floor, Hacking Tool on the fourth floor, and a bunch of other good items. On the final floor, I got a Meteor at the shop to buy and switch to, now that I was at Level 8. As I mentioned above, even with all those advantages it was still a tough fight. I restarted floors many times over the course of a few hours to make sure I progressed as safely as possible, and I still had to restart the Athena floor because of failing at the boss fight over five times. My point is that even with really good RNG, you're still going to need to "get good" to an extent, learning enemy and boss attack patterns to get through as much as possible without getting hit.

Once you beat Athena, the achievement will unlock immediately, and you can breathe easy know the hardest is behind you.