Achievement Unlocked

Complete Chapter 1 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 2 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 3 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 4 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 5 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 6 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 7 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 8 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 9 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 10 on any difficulty setting

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Storyline achievement. This will unlock once you get in the tram heading for the next chapter.

Complete Chapter 11 on any difficulty setting

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Storyline achievement. This will unlock once you get in the space ship heading for the colony.

Complete Chapter 12 on any difficulty setting

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Storyline achievement. This will unlock once you get in the space ship escaping from the colony.

Complete the game on the hardest difficulty setting

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Without a doubt the hardest achievement in the game. In the beginning you will most of the time be a sitting duck, with little ammo, crappy armor, crappy weapons. You should concentrate on getting the most ammo possible. Use Stasis often to slow down enemies in stressful situations, and concentrate on one at a time. Stasis is also great against single enemies, as you can slow them down and then swing/stomp to dismember their limbs. Ammo conservation and health packs are keys for survival.
Upgrade your suit and the Plasma Cutter simultaneously. Then equipment and other weapons. The Line Gun, the Ripper and the Pulse Rifle can prove to be useful. Also, you could use the Military Suit glitch if you've completing the game on a second playthrough and thinking about going for Epic Tier 3 Engineer on your next. To glitch it, you will have to complete two playthroughs on the same difficulty (easy/medium/hard), and once you've completed your second playthrough, skip the credits and do not save. Immediately start a new game on Insane, and you should quickly see if the glitch worked. If it did, then yay! You now have a better armor and more inventory space.

Cheats
There are a few cheats that can help you on the way, some works only once but some works all the time. Hit Pause whenever while in game and press the button combinations listed below for some rewards.
Works once
Y, X, X, X, Y - 2 Nodes
Y, X, Y, X, X, Y, X, X, Y, X, X, Y - 5 Nodes
X, X, X, Y, X - 1,000 credits
X, X, X, Y, Y - 2,000 credits
X, X, X, Y, X, Y - 5,000 credits
X, Y, Y, Y, X, X, Y - 10,000 credits

Always works
X, X, Y, Y, Y - Refills oxygen
X, Y, Y, X, Y - Refills Stasis

Complete the game on any difficulty setting

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Storyline achievement. This will unlock with Exodus once you complete the game.

Store 25 Items in the Safe

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When you get items you don't have any use for (e.g. ammo for weapons you don't have, etc.), do not sell them in the store. Instead, when at the store, you are given the option to store them in the safe. Just store 25 different items in the store to unlock the achievement.

Collect 75 Logs

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See Legend Teller

Collect 150 Logs

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Collecting 150 Logs is actually not as hard as it might sound. In total, there are 168 Logs you can get throughout the game, but you do not have to actually pick up 150 Logs. You will obtain logs whenever someone speaks to you through audio or video (for example when you are in contact with Hammond or Kendra.) Although, you should pick up each Log (text/audio/video) you see lying on the ground, to be sure you can get the achievement.

Own every Weapon in the game

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Once you get the schematics for the weapons, you might want to buy the weapons themselves. If you have no use for it, just move it over to the safe. You will need the schematics for each weapons and 55,000 credits to buy them.

Note
Buying the weapons while going for One Gun will not affect the achievements, so feel free to go for both in one playthrough.

Complete Level 6 in Zero-G Basketball

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Zero-G Basketball is in Chapter 10. You are required by the storyline to go to the Zero-G Basketball court in order to obtain a Nav Card, so you can't miss it. Once you have obtained the Nav Card, you will have to activate the game on the first platform when coming from the lockers. This will start the first level of Zero-G B-ball. Jump to the platform closest to the hoops. The ball will be launched from the wall, and you will have to pick it up using kinesis. The objective of the game is to shoot it into the colored hole in the wall which is lit up.
Whenever a game finishes, simply hop back to the first platform and re-activate the game. Once you've completed Level 6, the achievement will unlock.

Note
For each Level completed, you will unlock reward lockers in the locker room, so make sure you pick these up when you are finished.

Collect 8 schematics

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Whenever you see a schematic (they're the blue, glowing sheets you find lying around), pick them up. They provide new items in the store, such as new suit, new weapons, etc. Once you've picked up 8 in total, the achievement will unlock.

Shoot 50 objects using Kinesis

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When you obtain Kinesis, just pick up 50 random objects (using B while in aim mode), and shoot them off (using the Right Triggr).

Dismember 20 Limbs

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See Butcher

Dismember 500 Limbs

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See Butcher

Dismember 1000 Limbs

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This could take more than one playthrough, depending on how you play. The way I did it was to kill an alien, and once he was down I stomped all of his limbs off (legs, arms, head) using the Right Bumper. This also works on dead bodies you find lying around. If they are hanging in the air, use Right Trigger while not in aim mode to do a ridiculously strong arm swing, which will dismember limbs.

Use Stasis on 50 enemies

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Stasis is used in aim mode when pressing X. Stasis will slow down any enemy or object you use it on, but you have a limited amount of it, so you might not want to spam it mindlessly. Sometimes, you will have to use Stasis you proceed from an area, but in these areas, Stasis re-fill stations are available.
While playing the game on harder difficulties (Hard/Impossible), you might want to save Stasis for stressful situations (where you have several incoming enemies, and you run out of ammo, for example).

Note
There's a Stasis re-fill cheat if you need it. Hit pause and press X, Y, Y, X, Y, and after hearing a short sound, Stasis will re-fill when unpausing.

Achieve a perfect score in the Shooting Gallery

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The Shooting Gallery is in Chapter 9 when you've boarded the Valor. In the Shooting Gallery, there will be some red and blue man-shaped 'boards' popping up. The objective is to shoot all of the red boards, and none of the blue. If you miss a red one, or shoot a blue one, just walk all the way back of the room to reset the game, since you will not able to meet the requirements anyway. The gun you are using here is the Plasma Cutter, and do not worry about ammo, it's unlimited for the minigame.

Zero-G Jump over 100 times

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When you are in a Zero-Gravity environment, in aim mode, press Y to Zero-G Jump. Your ammo indicator will flash red if Isaac cannot jump to the location you're aiming at, so if that happens, pick another one.
I did this on Chapter 2, in the Zero-G Therapy chamber. Just jump constantly, and eventually the achievement will unlock.

Beat the game using only the Plasma Cutter

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This achievement is easier than it sounds. The Plasma Cutter is probably the best weapon in the game, and depending on the difficulty level you're playing on, this achievement will be a breeze. I chose to unlock it by playing on Medium, but many people are combining this with Epic Tier 3 Engineer.

You would want to stack up on only ammo for the Plasma Cutter and health packs. You should sell anything else, and buy power nodes for the cash (or weapons, if you need Full Arsenal.) Upgrade the Plasma Cutter all the way, and you should have no problems killing enemies.

Kill at least 30 enemies with a melee attack

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You can use the Right Trigger to swing at them till the enemies die (use Stasis to slow them down), or you could first shoot their legs off, then stomp on them till they die. The latter is the easiest way.

Upgrade all weapons and equipment

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You will have to upgrade each weapon, your armor, stasis module, and kinesis module. This will take more than one playthrough. If you go for One Gun in the first playthrough, start a new game on the same difficulty to start off with every piece of equipment (armor, weapons, power nodes, credits, etc) from the last playthrough. Then just play until you get enough power nodes to upgrade everything.

Force an enemy in a Gravity Panel 5 times

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There are a few missing Gravity Panels on Chapter 4 and a few on Chapter 9. You can identify the panels by the blue beams coming up from the floor where there appears to be missing tiles. Be careful not to walk onto them, because it will push you upwards into the roof and squash you. You can force the enemies by melee attacking them until they touch the beam and gets killed (use Stasis to slow them down.)

Note
It appears that you don't actively have to push them. I got this achievement on Chapter 4 without pushing a single enemy on to the field. They just walked there themselves and got killed.

Spend 300,000 credits at the store

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This will most likely unlock during your first playthrough. You will most likely be buying stuff anyway, so just let it unlock naturally, instead of spending alot of credits on useless crap!

Kill 30 enemies with the Contact Beam

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See Eviscerator

Kill 30 enemies with the Ripper

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See Eviscerator

Kill 30 enemies with the Plasma Cutter

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See Eviscerator

Kill 30 enemies with the Force Gun

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See Eviscerator

Kill 30 enemies with the Flamethrower

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See Eviscerator

Kill 30 enemies with the Pulse Rifle

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See Eviscerator

Kill 30 enemies with the Line Gun

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Every Kill 30 enemies with the [weapon] achievement is pretty easy to get. The only problem is getting the ammo for the guns. Some of them are expensive, but whenever you kill an enemy, it might randomly drop ammo for whichever weapon you carry in your inventory. Otherwise, open each container, smash every box, etc., to get as much ammo as you can. If you find ammo for a weapon you have yet to unlock the achievement for, store it in the safe, ammo for weapons you've already unlocked the achievement for, sell it.

I would recommend that you get these on the playthrough in which you get the Maxed Out achievement. If you're going for One Gun, you will obviously only get Tool Time.

Find the Peng Treasure

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The Peng Treasure is located out-of-reach in the area where your crew lands with the Kellion. In Chapter 1, you are unable to get it, because you need the Kinesis module which you won't get before Chapter 2. But you return to this area in Chapter 11, with the Kinesis module, so that is when you are picking it up. It's on the opposite side of the ramp where the Kellion was docked. Just look for a glowing object.

The Peng Treasure is worth good 30,000 credits, so it will come in handy at the store.

Kill a Brute

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You won't be fighting a Brute until Chapter 4. On the easier difficulty levels, killing the brutes aren't that challenging. However, on the harder difficulties, you might want to use some tactics. Keep in mind that their weak spots are their shoulders and their back. If you hit them enough, they will curl up, so you can run behind them and shoot them in their back.

Note
Using Stasis works well on them, so make sure you take advantage of that!

Survive the ADS Cannon with over 50% shield strength remaining

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This achievement is hard for some, and easy for others. I've heard about people spending hours on trying to unlock this, but myself I got it in 5 minutes. There's a save point right before you jump on the cannon, so make sure you save! Also, you would want to turn up Brightness in the Options as far as it goes, as this will help you see the rocks for a farther distance. If the shield strength drops down below 50%, just reload the game and try again.

Catch a Brute or Leviathan Pod using Kinesis

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To catch a Pod, use Kinesis (aim at the Pod, and press B while in aim mode.) The Brute won't fire a Pod at you unless you've dismembered one of his limbs. I got this against the Leviathan, as firing it's Pods back at it is a good and easy way of beating him.

Kill the Leviathan

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The Leviathan is the enormous beast covering up a hole in the ship on Chapter 6. The Leviathan's attacks goes in two cycles. First, it attacks you with three tentacles (although, only one at a time!) The tentacle it attacks you with swipes horizontally in the area in which you are standing. You can either use Zero-G jumps to avoid getting hit, or shoot the tentacle's weak spot (the yellow bag-like thing at the base of the tentacle.)

Once you've shot off each tentacle, the mouth will open up and reveal it's weakest spot, and shoot out Pods from it. Here's where Playing Catch is unlocked. Allow it to shoot one pod at you, catch it with Kinesis, and shoot it back. You can also just shoot the pods when they're in his mouth if you've already got the achievement.

Kill the Slug Boss

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The Slug Boss is the gargantuan (hah! Finally got to use that word) alien on the hull of the ship in Chapter 8. Make sure you save before this battle, so that you can unlock Slugger at the same time!
The boss is actually not that hard, but the beginning can be stressful. It has 5 tentacles that throw objects at you. You will have to hit each tentacle's weak spot (once again the yellow bags at the base of the tentacles) to dismemeber them. It will retract it's tentacles from time to time, which is a good thing, because it gives you time to focus on the other ones. Try to shoot off one by one instead of going for all. You can shoot the objects it throws at you if you get the time.
Once you've shot off all 5 tentacles, the boss will float out into space. If you have more than 50% shield strength, you will also get Slugger.

Kill the Slug Boss with more than 50% shield strength remaining

Guide
See Get off my ship!

Escape from a Lurker's grab attack 10 times

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A Lurker is a necromorph made from a baby, the ones with the three tentacles that shoot towards you. To make a Lurker grab you, you will have to run up to them. Sometimes when you approach them, they will just retreat from you, but just follow them until they grab you. Once you are grabbed, tap A to escape from the grab.

Note
For some reason, they won't grab you in zero gravity environments, so nevermind trying to get grabbed there. At least no Lurker cared about grabbing me when I tried to get them to grab me.

Kill the Hive Mind

Guide
The Hive Mind is the last enemy you fight in the game (the final boss!) and it's on Chapter 12. It is ridiculously easy, and unless you run out of ammo completely, you should have absolutely no problem beating it.

It's attack is a tentacle swing which you can dodge by strafing. Just strafe left and right, and when you see it goes a little backwards to launch it's tentacle swipe, move as far left or right as you can (depending on which side is the closest), and then move to the opposite side when it swipes to avoid getting hit. Once it's swiped at you a couple of times, it will roar at you, allowing you to shoot the yellow sacks. Once you've got 1 left, he will grab you. This is actually a little hard, because you will have to shoot the last sack while grabbed. Just make sure you don't get disoriented by the fact that you are hanging upside-down, because the way you aim is still the same (you do not have to turn your controller upside-down too!)

Once you've shot all of the sacks, he will still swipe at you, but this time the yellow sacks are in his chest. Once he's swiped at you a few times, he will open up his chest, which will allow you to shoot the sacks there. And once those are all gone, he will fall down, and you can safely escape to the ship.