Walkthrough that will get you ALL OF THE achievements, notes at the END of the guide for some.
Directions in this will be UP, DOWN, LEFT, RIGHT, etc. Some may be "UP/LEFT" to help find the sweet spot on the screen.
Double clicking on an exit to another screen will cut the walking animation, and simply load the next screen/cutscene.
Standing recommendations:
• Talk to everything you can. Use EVERY dialogue option there is. Learn all you can. I won’t mention this again in most cases, but towards the “every death” achievement, and whatnot? You need to do this.
• Click EVERYTHING. Right-click first to examine, then actually click to interact however you can. You’ll learn a lot.
• Unless you’re in a sequence that needs tight timing, mouse around. What you find might surprise you.
Also, standing warnings: themes of suicide, death, loss, depression, clowns, and other bleakness. This guide is also MADE of spoilers.
You’ve been warned.
Final recommendation: If you play through this, and feel like you missed something important, play it again with annotations and/or commentary enabled. It gives insight from the creators, and may help fill in gaps if your exploration didn't give you the depth you feel it should have.

With that said, this walkthrough is going to have the playthrough for all the achievements, including EVERY. WAY. TO. DIE. If you don't want that achievement, you may ignore some lines.
Noted again at the end, you cannot 100% in a single run, as two achievements are mutually exclusive.

When the game opens, you’ll automatically walk to the clown. Listen to what he says, ask all your questions. Examine the area.
Eventually, go into the MOUTH.
Look around the well area.
Jump in (use) the well. You will have to click a couple times.
Once you respawn, pick up the ROCKS.
Talk to the BIRD (you have to throw a rock at it, but don't worry, you don't run out of rocks as far as I've been able to tell ever), talk to MURMUR, don’t bother with the phone yet.
Go UP.
Interact with the HOLE.
Take the RAT.
Go LEFT.
Interact with the GUN.
To win, you click the target on the lit skull. They move fast. There IS an achievement (Sharpest Shooter) for getting this on the default (fastest) speed. If you cannot after a few tries, there are steps to take. This will be covered later in a **** section. In the achievements section at the end of this guide, take note of a death you may miss if you get this achievement.
Once the DRAWER is open, interact, take the BOTTLE.
Go RIGHT, then DOWN. You will automatically answer the PHONE. This will happen whenever it rings and you’re at the well. You may see the *ring* from a screen near the well, notifying you to go take a call. When this happens, do so.
You can dial 0 at any time for the operator for hints. Dialing once at the beginning and talking to the operator may or may not be needed for the talking to everyone achievement, I did it, early on, before a hint was needed.
Go UP, then RIGHT.
Meet the old man. Find out he’s Fimbul Fambi (hereafter FF).
Talk to FF. While talking to him, when he asks about the DOVES, say YES.
Pick up the MEAT (“BREAD”).
Exit to the LEFT, then DOWN to the well.
From the well, go LEFT.
Talk to 83. Make sure you badger him to make you something until he burns you to death. Return to his screen after this is done and you respawn.
Go LEFT again.
Pet the BLACK DOG.
Return to that screen after you respawn.
Give the MEAT to the DOG, pick up the SPIKE.
****IF you could not do the shooting gallery, AND to get the death related to it, here’s what follows:
Return to the Shooting Gallery screen.
Use the SPIKE on the CONTROL PANEL.
Look at the COVER.
Interact with the bare PANEL.
***Adjust wrong once to die that way for the achievement, if you’re after that, then travel back to the gallery screen.
Adjust the HANDS to all within the safe ranges (lit), but the far right hand should be at the very far right of the lit area.
Hit the BUTTON.
Play the game again (GUN) and get the BOTTLE.****
Return to FF, ask for more BREAD.
Pick up MEAT.
Throw a STONE at the RAVEN, on the larger interaction aim for the HEAD.
Take the “BEAK” note.
Throw another STONE, at the RAVEN, this time at the FEET.
Take the “CLAWS” note.
Go LEFT, DOWN to the well, then LEFT once to 83.
Place the SPIKE on the ANVIL.
Give BEAK to 83. You will automatically pick up the DAGGER.
Use the DAGGER on yourself for the deaths achievement.
Use DAGGER on RAT in your INVENTORY. You will get RAT SKIN and COINS.
If you want the Heads I Win achievement, flip the coin by using it on yourself until the achievement is granted. It takes a good few flips to pop.
Use BOTTLE with MEAT in your INVENTORY, you will get TAINTED MEAT and EMPTY BOTTLE.
Return to the well area.
Use COINS with MURMUR. We’re going to do this three times, and get all our fates in order now.
***If you want the achievement later, take notes on which options you picked. Knowing a little about Tarot and card meanings, I used:
Past: Hermit > Star > Empress
Present: Hanged Man > Wheel > Heirophant
Future: Fool > Judgement > Death
*****During Future, there are numbers given. Subtitles help with this a LOT if you have any trouble catching them.
Immediately after Future, you’re given the hint to make a call.
First, go RIGHT.
Look at the PICTURE.
Get the PHONE NUMBER – 431-1013 (it is the rest of the number you got during Future).
Return LEFT to the well.
Use the PHONE.
Dial the number above.
When asked, say YES.
Go LEFT, LEFT, UP (leftish).
Talk to the MASQUETTES.
For the death related to them, ask to look under their masks until you die. Respawn, and return to their screen.
Interact with the CAR.
At the top, click the BAR on the cage. This is another death, but unavoidable.
••••SOME TIME AFTER THIS, a box will appear on a random screen. There are two achievements related to this box. Please refer to the final guide section for information on these achievements!!••••
After the cutscene, LEFT, MOUTH, UP, LEFT.
Talk to FF, ask for more BREAD.
Pick up MEAT.
Pick up BRANCH.
Use DAGGER on NOOSE to get ROPE.
LEFT and DOWN to the well.
LEFT to 83.
Place BAR on ANVIL, give CLAWS note to 83.
Use ROPE on CLAWS in your INVENTORY, make a GRAPPLE.
RIGHT to the well.
RIGHT, RIGHT to the area with the electrified fence.
Touch the electric fence. Once you respawn, return to this screen.
Use GRAPPLE on LEVER.
Open GATE.
ENTER.
Read all three PLAQUES.
Activate the BLACK SWAN.
Interact to break the glass.
Interact to take the HEAD.
Use HEAD on BRANCH in your INVENTORY.
Interact with the STREAMMAID. To activate, the sequence is:
XOXX
XXXO
OXXX
XXOX
(With the O being the button you push)
Talk to the STREAMMAID about everything.
When she starts repeating about the WEAPON, show her the DAGGER. You can do nothing more with her just yet.
Interact with the ANGRY CREATURE on the left. You want to anger it.
In no particular order, the following words will anger it (this list may not be complete, obviously, please comment below if you find more I need to add):
• ASH
• IDIOT
• PENTAGRAM
• VOMIT
• SPONGE
• MAGIC
• MOLD
• PRIMITIVE
Make your way back to where you died (MOUTH, RIGHT, RIGHT)
Use the BOTTLE on the ACID.
LEFT, LEFT, LEFT.
Use BRANCH with 83 to get a TORCH.
******Using this TORCH on ALL things will help with the achievement later.
RIGHT to the well.
Use TORCH on RAT SKIN in your INVENTORY.
GRAPLE on WELL, click WELL to go in.
ACID on GRUB.
DAGGER on GRUB.
Click CICADA.
Use TORCH on CAGE. Talk to ROTTA.
After dialogue begins to repeat, give RAT SKIN to ROTTA.
CICADA, ROPE, RIGHT, RIGHT.
Talk to STREAMMAID, give her her name (NINEVEH).
Use TORCH on BLACK SWAN, STREAMMAID, and CREATURE.
LEFT, LEFT back to well.
Down the WELL, back to ROTTA.
Use TORCH on ROTTA.
Use SHARPENED DAGGER on KNOT.
Take HAIR.
CICADA, ROPE.
Use the TORCH on MURMUR.
UP, LEFT.
Use the TORCH on the SHOOTING GALLERY.
RIGHT to the tent.
Use the SHARPENED DAGGER on HOLE.
Enter HOLE.
Use MEAT on TERATOMA MOUTH.
Close the close-up, DOWN to exit.
RIGHT to FF, ask for more BREAD.
Take MEAT.
LEFT, HOLE.
Interact with TERATOMA.
Give MEAT to another MOUTH.
This will automate the sequence.
Once done, take EYE.
CLOSE, EXIT (DOWN), RIGHT.
Give EYE to FF.
Throw one last STONE at the RAVEN, aim for the BODY.
Take the “WINGS” note.
Use TORCH on FF.
LEFT, DOWN, LEFT to 83.
Use HAIR on ANVIL.
Use TORCH on 83.
Use “WINGS” note on 83.
*******NOTE: This is your LAST chance to get all the spirits.****
For the deaths achievement, at some point after this, when the Dark Thing appears at random, don't flee, just let it kill you on that screen. Average is about 20 seconds, it seems.
LEFT, LEFT.
Interact with the CAR to open the hood.
In the close-up, use TORCH on all SPIRIT LAMPS.
Use the CAR.
At the GAP, for the deaths achievement, first just try to jump.
**********NOTE: If you do NOT get "Joke's on You" at this time, STOP. Keep dying in various ways until the achievement pops. You CANNOT get it once you proceed. You will have to restart/restore to get it after this point.**********
After respawn, and return to that screen, use the WINGS on YOURSELF.
When grabbed by the CRAB, the first time, sit there, after a couple minutes, it will kill you.
After respawn, and return to it, the second time, reasonably quickly, use ACID on the CLAW.
Use TORCH on EYES.
Use KNIFE on MAW.
Welcome to DEADLAND, headless wonder.

You’ll automatically go LEFT.
MOUTH
Talk to the you-headed-RAVEN at the well screen (again, you may need to throw a rock at it in which case wait until after the FERAL HUMAN below, then toss a rock and talk to it).
Talk to your own head at the well screen.
Go RIGHT.
Pick up LIMB.
LEFT to well, use LIMB on BOX.
Jump into the central PIT.
As the screen changes, click the lighter dot (white dot/shape) to spin towards it. THERE IS NO INTERACTIVE MOUSEOVER/TOOLTIP.
Eventually, it’ll show as the CICADA, flying you to safety with words of wisdom (and some vague hinting at the plot of this game).
Go LEFT, LEFT, talk with the….FERAL HUMAN to die.
Get the ROCKS.
LEFT, MOUTH, UP, RIGHT.
Talk to….yourself as the scribe.
Pet the SNAKE. After respawn, return to this same screen.
Throw STONE at RAVEN?, aim for the HEAD.
Take “TOOTH” note.
LEFT, LEFT to the Shooting Gallery.
Throw a STONE in, to open the closer view. TALK to the skulls before throwing more rocks.
You have to throw stones to align the skills so power flows not only into each, but through, connecting the wispy ends. Screenshot below shows what this should EVENTUALLY look like.
Take the BOTTLE from the DRAWER (you may have to walk to the side to click it, you’re in your own way).
RIGHT, DOWN.
Use BOTTLE on REGURGITANT.
LEFT.
Speak to SKULL. Its EITRI. Talk to EITRI until all dialogue is exhausted.
Use REGURGITANT on NODULE.
Use LIMB on EITRI.
Use “TOOTH” note on EITRI, you’ll automatically take the KNIFE.
Use the KNIFE on yourself (I don't recall if this works or not).
LEFT to the well, UP.
Interact with WEBS.
Use KNIFE on WEBS.
Take the HOMUNCULUS.
CLOSE the interactive window.
RIGHT to the tree.
Use BOTTLE on BRANCH.
Take FULL BOTTLE after a couple drips.
Drink the snake's poison for that death.
Use POISON with HOMUNCULUS.
• LEFT, DOWN, LEFT, LEFT to FERAL HUMAN (from SCRIBE-YOU).
• LEFT, MOUTH, LEFT, LEFT to FERAL HUMAN (from respawn).
Give TAINTED HOMUNCULUS to FERAL HUMAN.
LEFT/UP.
Speak to the trio of yourself, PAST-YOU, PRESENT-YOU, and FUTURE-YOU.
For the achievement, if you used my options, its: Past=HERMIT, Present=HANGED MAN, Future=FOOL; or consult your notes from your choices.
********You can also say you don’t remember and still get through, you just don't get the Know Thyself achievement.
Walk up the TRACKS.
Use ROCKS on MIRRORS (not the broken ones).
Use KNIFE on EYE.
Inside, register as YOUR NAME (yes, literally).
RIGHT.
Interact with LIT MIRROR for information.
Exit RIGHT until POOL is full.
Use BOTTLE on POOL.
Use BOTTLE on YOURSELF.
Exit LEFT until LADDER appears (or you say one appeared), ensure you stop on the screen that has the ladder.
Interact with ORNATE MIRRORS (there are three).
In each mirror, click the SHARD to knock it loose, each mirror has three SHARDS.
Pick up SHARDS from the floor after each.
On the final mirror, one shard is separate, click it, it will fall.
Use the LADDER.
Collect the SHARD.
Use the LADDER again, exit LEFT.
Click the LIT MIRROR.
Use the on-screen controls to rotate shards, and place them in place.
Once the final one is in place, a PORTAL will appear.
Use the PORTAL.
Click the GATE.
*********Ever play LeChuck’s Revenge? If you did, this next bit will feel VERY familiar. *********
As you get to the next several scenes, you’ll have a couple seconds to click what you need. You will repeat through, no worries if you miss it a time or two. Once you have the KNIFE, you can use it on YOURSELF to save a few seconds per scene if you prefer.
In no particular order, you’ll need to do the following:
• Get the CLAWS from near Eitri.
• Get the DAGGER from near the Streammaid.
• Use the DAGGER on the NOOSE for the ROPE.
After you have all the necessary items, next chance do the following:
• Combine the CLAWS with the ROPE for the GRAPPLE.
• Use the GRAPPLE on the WINGS at the Valkyrie ride entrance.
Once all that is done, next time you’re at the GAP, use the WINGS on YOURSELF.
After the cutscenes, when its only the three of you left, SAVE YOUR GAME.
Talk to the WOMAN.
Talk to the SHADOW.
There are four possible endings I’ve found so far, by doing each of the following, three of which are deaths:
• Jump off the EDGE (upper left back bit).
• Use KNIFE on DARK THING.
• Use KNIFE on YOURSELF.
• Use ORB on YOURSELF.

These are largely integrated into the walkthrough, but here they are noted for convenience, and a further explanation on the BOX achievements:
As said before, please note, some of these are going to require two plays through the game - you cannot get Pandora AND Unobtanium in the same game, they are mutually exclusive.

After you release the Dark Thing, a box will appear in any of several screens.
• PANDORA achievement requires you open the box.
• UBOBTANIUM achievement requires you resist the box, and do not open it. If you pick up the box, you MUST use the inventory screen to cycle items from that point, or the box may open. Once you reach Deadland, the achievement should appear.

For the Dumb Ways to Die achievement, in the APPROXIMATE order they will appear in the guide:
• Jump into the well before you have the grapple set on it.
• Badger 83 to make you something until he burns you to ash.
• Pet the Black Dog.
• Mis-set the control box of the Shooting Gallery. (notes in the walkthrough).
• Use the Knife on yourself.
• Touch the electric fence.
• Get spit on by the angry creature.
• Ask to see under the Masquette's masks....
• Fall after releasing the Dark Thing.
• On the Dark Thing's random appearance, don't run, let it kill you (takes about 20 seconds on average to happen).
• Try to jump the gap without wings.
(This SHOULD get you Joke's on You here, but if it doesn't, just repeat a couple deaths until it does. If you get to Deadland without getting this achievement, you have to restart/restore.)
• Just sit in the crab's claws until you die (takes a solid couple minutes).
• Pet the snake.
• Drink the snake's poison from the bottle.
• Pet the Feral Man.
• Get killed by the Shadow in the end scene(s).

For the Big Talker achievement, make sure you talk to (not just automatic dialogue), in the APPROXIMATE order they will appear in the guide:
• Well Raven
• Murmur
• Fimbul Fambi
• 83
• Streammaid
• Angry creature (starfish thing)
• Rotta
• Masquettes
• Your own head
• Well You-Raven
• Shooting Gallery Skulls
• You-Scribe
• Eitri
• Feral Man
• You Trio (Past, Present, Future)
• Woman
I also talked to the Shadow and the Operator, not sure if these are needed, I've seen mixed responses.

Thank you to the kind commentators, and friends (that asked to remain anonymous for this guide) for the help and information on the additional achievements. You're the MVPs here!
Cheers! And I hope you love the game as much as I did!