Since there is only the story mode we will start with that. I will go step by step, chapter by chapter and will explain what to do when, but one thing in advance is that you are NEVER allowed to skip anything! This is important since otherwise the achievements wont unlock.
You will start in a small room and have blurry vision. IGNORE the instructions to clear your vision and stumble blindly through the first part of the level. This is very short and shouldn't pose any problems at all. Just follow the orders and upon reaching the cutscene, your vision will clear and you get the following achievement:
The Blind Man
Finish the 'Wake Up' sequence without blinking.
Now get on the elevator and after the cutscene, make your way down the elevator shaft. Enter the building and get the fire extinguisher. Make your way to the guy trapped in the room, break the door, make your way through the fire and jump the gap. Now get to the next cutscene and enter the next room. Search the shelves for items, get to the wall and jump across to the previous room. Now you will have to jump to the restroom once more and after the cutscene, you will be at the facade of the building. Now proceed along until you hit a room, where you have to put the extinguisher on the platform and jump on the wire to lift it up. Extinguish and proceed through the rooms until you hit the next cutscene and end the chapter for the following achievement:
Finish the episode without skipping any sequence.
You will get a lot of the inventory-related achievements in this chapter, so I will go into detail on the earliest points you can get them.
Upon starting the chapter, we will start with a fight with the woman from the previous chapter. Damage her a little (there is a katana lying around as well to help) and after the fire descends, hold a chair in the fire to light it and then set the woman on fire to finish the fight. Now climb up the cable, jump across the gap and destroy the elevator doors. You will now encounter Sarah. After the cutscene, we will reach a new floor; just climb outside into the other elevator. Get outside and get the flashlight and a pack of ammunition, and to the right you will also find some glow sticks and an explosive bottle. Don't go anywhere further and stay in the elevator. If you still have the health spray on you, combine it with the tape for an achievement. If not don't worry, there will be ample opportunities for that later.
The Sticky Bomb
Take a bottle filled with flammable content or a spray and combine it with an adhesive.
Now use the tape on the bottle for another achievement:
Now combine the first aid spray with the box of ammunition for another achievement:
Detach the spray from the ammunition and combine it now with one of the glow sticks:
The Glowstick Bomb
Combine a taped bottle filled with flammable content or a spray with a glowstick.
Now combine the bottle with your gun and you get fire bullets:
Make a fire bullet by pouring flammable liquid on it.
Get the bottle in one hand and the weapon in the other hand. Now throw the bottle and shoot it in midair for another achievement. After that, reload the game so you have all the items still in your inventory.
The Air Bomb
Throw a bottle filled with flammable liquid and shoot it mid-air.
Now head forward a little bit to encounter Ratz (small crawling creatures). Unequip everything you have, got to the ego perspective and once you are close to one of them, push resulting in you kicking them away. Continue this 10 times and an achievement unlocks for you:
Go to the right inside the small office-like room and short fuse the electricity. After a cutscene you will have to fight a Humanz. Now take out your fire bullets and shoot its fissure (either part of it will count and suffice). Upon doing that, another achievement will unlock:
Finish off a Humanz by shooting fire bullets at it's fissure.
Take the door to the left now (door combination is 943) and after the cutscene, dispose of the new enemy. Now head onwards, extinguish the flame and enter the garage for another cutscene. Now walk up to the car in front of you and shoot the window on the driver side. Enter the car for an achievement there:
Now get inside and check the sun visor above the seat. There should be a pair of keys right there, if not simply die and reload from the last checkpoint. This will grant you another achievement, but don't worry, this isn't the only place you can get this.
After that we will try to hot wire the car to earn another achievement. However, its most likely that the Humanz will throw you out of the car so make sure that before you attempt this, you quick button the gun and any exploding bottle (i recommend the one with the biggest damage).
Hotwire a car.
Now go outside and try to crowd them together as close as possible, throw the bottle in the middle, shoot it in midair and you get another achievement if you killed them all. If not, just kill yourself and reload (do the same if you managed to kill them, preferably set the car on fire and sit in it).
Kill 3 Humanz at once.
Now take the car and make your way through the garage. After the big jump, your car will be busted and you will have to go by foot. Get the lighter, get back to the car and burn the line of liquid to blow it up. At the end you should spot a taxi behind a busted metal door. Use fire to burn the log blocking the door and the darkness fissure will attack you again. Now you have two ways to get an achievement here. The first and maybe harder one is to pull out your fire bullets and shoot the fissure before it reaches you. The 2nd one will be to run to the left of the now-burning log and run straight into the fire. You will die, but so will the fissure as well. Either way, you get an achievement for burning a fissure. At any cost, KEEP the spray can with the pesticides!
Get inside the yellow cab, through the metal door and the next door to the right and make your way outside. Now you are on 59th street and you can get another two achievements. The first will be to make it down the street to the park in cockpit view. BEFORE you even think of using the accelerator pedal, change to cockpit view with and make your way down to central park. This is rather tough and you will have to repeat it a few times to get knowledge of the ways to take.
Drive all the way down 59th street in Cockpit view.
While doing that, the achievement for driving 10 miles should also unlock. It's also one of the earliest places you can get it, so i recommend getting it here.
Upon reaching the central park, after the last cutscene and the credits roll, the achievement for mastering this chapter without skipping any cutscene unlocks:
Finish the episode without skipping any sequence.
Upon starting the 3rd chapter, you get finally access to your PDA. Get to the contacts list and call all numbers available. Now call 911 and even though the other numbers wont respond, you still will unlock the achievement for doing so:
Now you will have your first encounter with the Vampirz. Equip your spray can with the lighter and burn one of them for an achievement:
Burn one of the Vampirz.
Now get inside the toilet (marked on your map as a red dot), get to the first-aid station, and take care of your wound. Another achievement will unlock:
Now get a wick and combine it with the bottle with burnable fluid for another achievement:
You will be in the toilet and the electrical cable will block your path. Run into the cable until you bleed again, take care of your wound with the bandages and rinse and repeat five times for another achievement. Now run into it until you die and reload the checkpoint.
Now shoot down the cable, get through the wall to the left and descend. In the area with the Vampirz ,destroy the glass roof. At the school bus, bring the bodies to the back of it. At the platform, fight off the Humanz. Use the spray can and lighter combo for another achievement:
After the bus falls down, shoot the door above you to let a cable descend on your position. Follow the path, climb along the cliff (quick time event, push repeatedly) and enter the car. Check the passengers seat for a health spray and ammo, get outside, and climb up. Here we will get another two achievements. The first and definitely hardest one is to kill the fish down at the body. Simply pull out your weapon and shoot the small goldfish that's swimming down there. This is hard and it took me a lot of time.
In comparison, the next achievement is a piece of cake. Simply destroy the large fleshy-looking sack in front of you; this is a cocoon and will grant you the achievement for destroying one:
Get up the ladder and follow the path. After the cutscene, short fuse the electricity and do the same a little bit further along (Ratz here). Now get across the water over the cables to the right. Upon landing after the vent section, get to the right, get a pipe and bring the cable outside of the pool. Now get back and get a gas canister (a Humanz might spawn here) and blow up the door. After a short cutscene you will have to dwell through darkness and sadly this section is a nightmare. The flashlight doesn't provide enough light to help you out and sometimes it doesn't scare the darkness away at all, resulting in a painful death. However, i found a neat little trick! Simply use the flashlight AND the lighter and use both all the time until you make it through to the right. Now continue and you will see in front of you a fire blocking your path and to your left a hallway area with electrically-charged water. You can see there is also a fleshy construct spiting out Ratz. Burn it to get an achievement, pull the cable out of the water and deactivate the 2nd fire.
Get through, take the tree log (the only tree log lying there), set it on fire, then get back and head to the right up the ladder. Deactivate the power just to take the cable and put it near the fence. Now activate it again to roast the Vampirz and continue up the ladder to reach Central Park. Here you will face a lot of Humanz as random encounters, so stay on your guard and always have something nasty exploding or fire with you. Check your map and you can see a circular area with static. This place is marking roots of evil, which are inside a house. Follow my collectables guide (next page) to get the first roots in the game and the corresponding achievement:
In the basement of the same building I found an emergency flare. Outside you will find a bottle (which bottle doesn't mater) and a wick. Now empty the bottle (pour the liquid over the bullets until its empty), use the double-sided tape, the wick and the emergency flare on the empty bottle for another achievement. Don't forget to combine the blood pack with the adhesive to get a combination for another achievement.
Combine an empty taped bottle with a wick and an emergency flare.
Grab one of the cars and head to the part where it seems as if a small piece of land is leading across the big gap. Make way and jump across (you will need to ram debris away) to reach the ambulance car. After a cutscene, the chapter ends and nets you another achievement:
After the paramedic cutscene right at the beginning, run to the car (take a right before you reach the car for a new gun) and follow Sarah's directions. Drive as fast as you can because the Vampirz will attack you and drop you to your death if too many cling to your car (drive into obstacles if too many cling to you to shake them off). Try to stick to the main road for maximum speed. After some time a tree will crash down and the Vampirz will carry you with your car to their nest. This fight is rather easy, simply throw 4 explosives at the belly and detonate them with your gun. There are plenty of them lying around and also a lot of first aid sprays. Stock up after the fight and you also will have unlocked an achievement for fighting this enemy:
After the cutscene, get in the car to the right and make your way to the GPS location. Don't forget to collect the roots of evil, preferably before you end the chapter. After the next cutscene, get to the tow truck and drive it to the right-most spot of the fissure (you can see across the radar destination). Lift the ramp and shoot the locks. After the cutscene, get a car (another cutscene while doing this) and make your jump across the gap to the museum. Another achievement for the jump is awarded:
Jump across the gap using the tow truck.
Get through the main gate and get rid of the fissure attacking you. Jump across the gap to the right, shoot the casing of the fuse box, and short fuse it (red cables). You will get another cutscene where you get a call, get up using the platform and enter through the window in the toilets. A fissure will attack you, so get rid of it. Take the fire extinguisher out of the nearby room (locked door, open it however you see fit) and clear the fire blocking your path. After the call and a small cutscene showing a new enemy, get rid of him and past the fire. Bash open the door, follow the corridor and the chapter ends with another achievement for you:
As soon as the chapter starts, you have to free Sarah from the flesh sack with the axe. After the cutscene you have to revive her, and as soon as you're done, you'll get an achievement for doing so:
Just a small hint, you will find a knife in one of the kitchens. Keep it for another achievement later in the game. You will find plenty of them in other areas, but just to be safe, i recommend keeping that one since it will spare you a lot of trouble!
Take the gas tank and use it as a flamethrower to burn the 2 Ratz nests and Ratz. Shoot down the cable from the cutscene, climb up (Ratz nest to your left) and burn the wooden barricades to the right. Get through, follow the path and after a cutscene, throw a molotov cocktail over the desolate wall to destroy the multiple nests and open the path ahead.
After this section, you'll come across another door and you’ll also get a quick cutscene showing you a Ratz running from a Ratz nest to drink some blood and then run back again. What you have to do is combine an explosive bottle with the sticky tape and a bandage/handkerchief to make a Molotov and throw it so it sticks to the Ratz. You have to time it so that it explodes next to the nest destroying it. I found that sticking it to the Ratz as soon as it starts drinking blood is a good measure of the right time to throw it. There are loads of bottles and materials to make Molotovs around the kitchen area, so if it takes a few goes, you should be well-equipped.
Upon reaching the big hall (Humanz will attack), get up the stairs to the left (more Humanz), and to the left to the guard behind the gate. Get through and make your way past the darkness corridor. After the cutscene with the guard, get in the elevator, get outside and encounter the boss. Shoot the lighting red marks on his body (1 on each shoulder, 1 in the belly region) and detonate bottles on him. Hide behind pillars when he uses his darkness attack (sign on the floor) and continue until he is dead. You will get another cutscene and an achievement:
Shoot down the sword to the left of the touch pad, cut off the guard's hand and continue until you reach a service entry. Open the latch, shoot down the cable, climb down, shoot the lock on the cage and get down to room 943 to end the chapter and earn another achievement.
Wait a little until Sarah tells you to stick close to her, do as she says and after the light, close your eyes to see Theophile's phantom. Follow the directions of his hand. He will point at things in the environment and you have to use the flashlight on the area he is pointing at. The first one is a newspaper article on the wall with ‘Sarah’ written on it. If you do it right, you’ll get a brief cutscene and Theophile will move to the next item; a record player. The third item is a door knocker on the other side of the room. The last item is a bottle with ‘Him’ written on it in the bathroom. After a cutscene where Sarah knocks you out, you talk to Theo and unlock another achievement:
Now follow the phantom again, get inside the hidden room and get the lens. Get outside and combine it with the flashlight on the wall (stand on the X on the floor). Follow that path, use the stapler to raise the bridge (recommend to take out the Ratz nests first), get across, raise the ramp in the next room and use the switch (Humanz spawn) to fix the ramp for you and your stapler. Get up (destroy the 2 nests again) and staple containers in a pyramidal fashion close to the ledge where the ladder broke down. Climb up, activate it, get across, activate the gate and lift it up with your stapler. Use the elevator up and after the cutscene, follow the light of the helicopter until another cutscene triggers and you finish the chapter, earning:
Finish the episode without skipping any sequence.
Climb up the cliff and evade debris from the helicopter. Go to the left inside the subway train and after falling down, climb all the way up and ahead to the subway station. Kill all the enemies in the area and go inside the train. Tentacles will lift you up and after some time, jump off the train and climb up the 2nd tentacle. Follow the fleshy path (looks like intestines of a big creature) until you reach central park again. Now we walk through central park, getting all the roots on the PDA that you can see.
Its time to get the combinations out of the way. There are two good locations for that; the first will be in the middle of the map where the big lake is. There is a building on the left side of the lake (the orange building just south of the black bit). It will be covered by a root of evil location and there are several roots inside the building. To get in, you need to blow open a door by throwing an explosive bottle and shooting it. The door is located towards the left of the building if you are facing it from its left side as it is on the map. There are 4 or 5 Humanz here so be prepared to take them out. This is also the best place to grind out the 100 Humanz kills if you didn't get them already. Simply run outside as soon as they are all done and rinse and repeat until it pops. There is an infinitely spawning medical spray in one of the rooms with a root in it, in a medical cabinet, which is very useful for restocking.
The 2nd location would be the building where you killed your first roots. There are always blood packs and water bottles which are not too hard to get but quite rare in comparison to other items. Combine everything following my list and the achievement will unlock. If it doesn't unlock, try manually reloading a flash light and a gun from your inventory to get it to unlock.
Get either a screwdriver or knife and an empty bottle. Head outside to a car, equip both, pierce the tank and refill your bottle for another achievement. Knives are scattered around the game, I stumbled across my first in the museum and simply kept it, and I found also 1 in the storage bunker.
Pierce a car gas tank and fill a bottle with the fuel.
Now follow the story marker. This will take you to a church where you have to light six symbols using your spectral vision, torch and lens like you did in Chapter 6. You will know you have successfully activated a symbol as you will get a small cutscene. The symbols can be annoying to activate even if you’ve lined up the torch correctly. I found that continuously blinking in and out of spectral vision helped. The symbols glow brighter if they are ‘activating’.
You’ll likely approach the church from the north. The first symbol is to your left on a wall in a small courtyard section with a bin in the corner. Go back to where you entered and go forward. The next one is on the corner of the building on the wall to the left of the wooden door. From this symbol, turn 180 degrees, go down the stairs and go left and keep using spectral vision to look at the wall to your left and you should find the third symbol. Now follow the church wall around to the right (if you are facing the symbol) and you’ll find some stairs that circle up in a half spiral. At the top of these stairs, some Humanz will attack you and the symbol will be directly ahead of you on the wall.
After this, go back to the wooden door and smash it down. There is fire and wood nearby if you want to burn it. In this next room is a painting. Destroy it and the symbol is behind it. Make sure none of the symbol is covered by the painting and ensure you are standing flat on the floor (no debris) when trying to activate it. Before going for the last symbol, make sure you have some exploding bottles and bullets as there is a tough enemy coming up.
The last symbol is in a room behind you but the floor is covered with the dark goo that eats you. Use your spectral vision to give you an idea of where you need to be standing and grab a chair and set it on fire or use glow sticks to get in here. There is also a window to the left of the symbol that you’lll want to jump through after activating it so bear this in mind.
Activate the symbol, jump out of the window and climb up to the roof. Battle with the camera to jump off in the right direction and when you land, get ready for the fight. The enemy will come out of the door in front of you. Throw a bottle at him quickly (maybe two) and then unload fire bullets at him until he dies. Go through the door, extinguish the fire to reach the platform and place the lens in the telescope and look at the moon to end the level and net another achievement.
Now we are at the last chapter and will unlock all the remaining achievements shortly. To begin, off we go for the remaining roots on the PDA. Upon getting them all, you should get the last corresponding achievements for that feat:
We should now have a full 100 spectral vision and therefore we should be able to find the hidden cave in central park. Go to marker on the map but be careful approaching it as there is a barrier surrounding it that you can only see when using spectral vision. Throw a Molotov over the barrier aiming for the reddish tree in the middle. This may take a few tries but there are handkerchiefs and bottles around so you should be fine. Once the tree has burnt down, you can pass through the barrier.
Head into the stone doorway, use the spectral vision to see the symbol, activate it and shoot down the rope from the flagpole in the middle of the room. Now follow the path down using the rope. When you get to the end, jump off to the left and then shimmy along the platform you land on to reach the next rope. Climb down and you will receive a call from Sarah. After this, continue down the dark passageway. Another short cutscene will trigger showing you the cave and you will unlock:
During the cutscene the scenery will light up revealing quite a decent view of nasty drops and tight ledges. Make your way down the side (flares light up upon getting close to them), activate the symbol (preserve flashlight for those!) and after the elevator sequence, enter the next room.
Use the board and place it in front of the light (you will flood the cracks with light), go straight forward, and rappel down the rope. Enter the next room and grab the block. The camera will pan out. Push the block into the light and you will see a large block on the left of the room lower to ground level. You will also see a low platform on the right of the room appear under the beam of light. What you need to do is push the block into the path of light on the far right of the room and then run to where the large block has lowered on the left. The result is that the platform will push the block out of the path of light and the block will raise with you on top of it so you can get to the door.
Get outside, rappel down the rope and follow the path downward. Once at the bottom, enter the next room, pick up the board and a cutscene will happen. Keep the board, run up to the first set of light rays (one on either side), and touch the right one with your board. Continue forward (be careful of the spikes), touch the left one and at the end, touch the right one to open the door.
In the next room, pick up the board on the next platform. The platform will start moving forward. Once you have control you can move the board into the light and it will stop the platform from moving. You will need to stop the platform just before crossing every obstacle to be safe - the platform moves very slowly.
Get down to the next room, pick up a wooden plank and set it on fire to burn the barriers. Move the unlit torch to the next trigger (don't worry about the falling debris, just try to be fast) to light it, pull it back so that the stairs lift, burn a log and burn the torch stand. Now run quickly to the other end of the room and get lifted up with the platform, get outside and climb down the rope.
In the next room, pick up the board and a cutscene will trigger showing you that the ceiling is closing down on you. You cannot see the floor but the path is marked on the ceiling above. You need to set the board on fire using the torch and then follow the path to the exit. Where possible, raise the board into the beams of light. This will stop the ceiling from moving and is necessary to reach the end in time. There are two split paths. At the first T junction, go left. When you are following the path down the left-most wall, go right at the first opportunity and follow the path to the exit. If you use the board to block the light while walking you should have plenty of time.
NB: Another method to cross this room, as per the video below, is to drop the board and follow the path laid out on the ceiling by looking directly up at it. At the T junction, go right instead of left and make a jump across the gap and then run to the finish. It’s quicker but may take several attempts.
Upon reaching the end, get outside to the next room and burn the torch stand in the middle of the room by picking up one of the torches. Make your way through the now open tunnel (there will a a cutscene), go back a few paces to where the torch starts flickering and drop it. Go back to the main room and get a piece of rock from the destroyed torch stand. Take it back to where the dropped torch is flickering and swing at the wall to your right to break it (another cutscene).
Back at Central Park, you’ll immediately be on a timer. Run to the marker and get in the car. You now need to race back to the museum. This is harder than it sounds since you have a limited time to do it and have to evade a series of spikes coming from below. Your best bet is trying to evade as much as possible and make good speed since the timer resets a few seconds if you do well enough. When you get near the destination, you’ll see a ramp ahead of you with fire on it. You need to hit the ramp at speed to the left of the fire. It’s a cutscene-style jump if you get it right and then you need to drive into the building through a tunnel to the car park. Get out of the car, run through the doorway and go all the way to the right. Draw your gun and shoot the lock on the bottom of the metal shutter in front of you.
There will be a short cutscene and and then you need to shoot the guy holding Sarah. I found this to be a pain and it only seemed to work if i shot his head when Sarah moves to the right. Time it right and you get another short cutscene.
Get in the room you got the lens from (there will be a cutscene), follow the story bits and at the end, either shoot or spare Sarah. You only have a few seconds to choose and there is one achievement for each choice. Simply reload that point and do the opposite to get both achievements. Upon completing this little cutscene, the game will end and net you your final achievements:
For those that might struggle, I also found a decent walkthrough for the whole game:
Congrats, you completed the game for a full 1000G!