These are related to the missable achievements.

• Demiurges (strong optional bosses) - make sure to keep either Andres or Ras'samrah alive (see map)

• Dark Wanderers (your clones) - you need to keep one alive - dont worry about this one since theres a clone fight behind the giant door to the north which you can ignore

• Cardinal Core dont interact with these yet, these are found after boss fights on round platforms (see image below). you'll also receive a sword after beating these bosses which you can pick up safely, but be careful not to walk to close to the core which is right behind the sword or you will be forced to interact with it.

Its probably a good idea to backup your save file now and then incase you mess up one of these.
save file location: C:\Users\username\AppData\Local\ShatteredTOTFK/Saved

With these things in mind you should progress through the world for a more spoiler free experience.
Come back to this guide once you are ready to progress past the giant door and clean up achievements.


The boss fight before a Cardinal Core will always be on a round platform like this.








The section after the boss fight.

showing location of cores and demiurges

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2429727735
Please follow this guide by Omega Ridley for the 6 ending achievements.

Beyond Slumber
Go beyond slumber


Awakening
Reach the Awakening


Loneliness of the Soul
Embrace the loneliness of the soul


All who wander are lost
Wander and get lost


Transcendence
Reach Transcendence


Digital Hazard
Remove the Heart of Limbo

Follower of orders
Destroy the Cardinal Cores


Risky gamble
Keep the Cardinal Cores


achieve both by reloading backup save file, since there is no ng+


Ergo sum
Kill all the Dark Wanderers

• 1. unmissable before you reach the open world.
  
• 2. in the open world.
  
• 3. in the open world, in front of Khotar entrance.
  
• 4. in the very last area progressing through Niphur.
  Niphur->Ras'Samrah caste->Imbolt?->wandere fight.
  
• 5. in frontier, area behind the giant gate.

The Enemy
Examine all the Strange Spheres


I'm sure i've missed some of the sphere locations, they should not be too hard to find tho.

• 1. in Niphur
  
• 2. in the open world, before Abandoned Bastion entrance.
  
• 3. in Frontier, can't miss it.
  
• 4. in Devesh, can't miss it.
  
• 5. in Myosis North, can't miss it.

Past future
Access the memorial archives


you need to remove all 4 cores and trade them in for a key in the hub area.
you will also need the limbo key which can be obtained after killing the final dark wandere.



The Great Lie
Find the Apocryphal Memorem


You need to finish Steh's questline to get a key which will unlock this area in Niphur.



The Collector
Collect every mask








These masks are dropped by enemies wearing them.
You will most likely be missing the Burning Hominculus Mask since these enemies are quite rare.
Burning Hominculus can be farmed in Niphur.
You can also visit the raven vendor in Niphur to see which masks you are missing.



Occultist
Learn all the spells


Ether Bolt

You get this after speaking to R'LYA for the first time in the tutorial area.



Aegis

This is dropped by the enemy wearing it, hard to miss.



Enhanced Ether Bolt

Received from R'LYA after giving her a Stolen Essence.



Void Cross

Received from R'LYA after giving her a Stolen Essence for the second time.



Oph

Can be purchased from Valnir for 4.000 essence.



Oph, Seerpent Blade

You will get this from Valnir after completing his questline.



Aksha, Coat of Shadows

Can be found in the last part of Abandoned Bastion. (see map)



Ras Algol, Ophidian Breath

Dropped by demiurge Andres.



Yed Prior, Serpent Fang

Can be found in Khotar, underneath a breakable floor.
see image below

You basicly just have to find them in all their locations and deplete their dialog.
Sometimes they will ask you to bring them a specific quest item.
They will only appear in some locations after you found them in a previous one.


The Lost
Bring Cenhelm to transcendence


Cenhelm's first location right after the first dark wandere fight.
Talk to him multiple times to deplete his dialog.

Cenhelm's second and final location in the dark fog city.
Deplete his dialog.
he will ask you to bring him "sign of the wail" quest item which can also be found in the dark fog city.


The Poet
Listen to Aesc's digressions


i probably missed some of the locations.

• 0. Before you reach the open world, cant miss him.
  
• 1. Right as you reach the open world.
  
• 2. In the dark fog city next to Cenhelm.
  
• 3. On the platform where the limbo well is (this is his final location).

The Warrior
Meet Naï before the end


i probably missed some of the locations. step 2 and 3 is the final steps tho.

• 1. Right as you reach the open world.
  
• 2. Next to the annoying platforming segment, he will ask you to bring him a weapon (i believe one of the bosses drops this quest item).
  
• 3. In Devesh, in front of the last red sphere.

The Lovers
Reunite Sorhen & Suur


i probably missed some of the locations.

• 1. Suur in Niphur.
  
• 2. Sorhen, he will ask you to bring him a pendant as proof (i think you get this from Suur in Niphur)
  
• 3. You can find Suur in Myosis North after completing step 2, he is near one of the limbo wells.

The Storyteller
Guard Stêh's memories


i probably missed some of the locations.

• 1. Right as you reach the open world.
  
• 2. In Imbolt (Niphur->Ras'Samrah castle->Imbolt)
  
• 3. In the open world, he is right next to a limbo well.
  
• 4. In the open world, on the same mountain top as Sorhen.
  
• 5. In the open world, near the entrance to Devesh where there is a bunch of Homunculus.
  
• 6. In Khotar after defeating Andres (not 100% sure about this one).

The Friend
Walk alongside Bakhti


i probably missed some of the locations. step 4, 5, 6 are the final ones tho.

• 1. Right as you reach the open world, she is next to the fast travel tower.
  
• 2. In the open world, standing under a tree.
  
• 3. In the open world, close to a limbo well.
  
• 4. In Khotar, next to the 2nd limbo well.
  
• 5. In Myosis North, next to the giant statue.
  
• 6. In the open world, near the limbo well.

The Mentor
Follow Valnir's teaching


i probably missed some of the locations.

• 1. Before you reach the open world, hard to miss.
  
• 2. Right as you reach the open world.
  
• 3. In the open world, in front of the entrance to Khotar.
  
• 4. In Khotar, after defeating Andres he will appear and ask for a quest item Andres dropped.
  
• 5. In the Frontier, next to the Portal door.

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2403111559
Please follow this guide by T3h Phish for the following collectibles achievements.

Old Soul
Forge the Sword of Remembrance
Requires 30 Memorial Shards to unlock and is found in the tutorial area.

Archivist
Read all the Memorem
You will need to remove all 4 Cardinal Cores to achieve this.

Medarch
Improve a weapon to the maximum
Requires 5 Segments of The Crucible to upgrade the forge.

Omega Catalyst
Increase the power and charges of the Catalyst to the maximum
Requires 9 Catalyst Charges and 4 Promethean Component.

These you should easily find on your own

King Rider
Complete the route in the Ancient Lands with the Espada
Beat the roller coaster platforming in the open world (see map)

At the beginning there was the King
Reach Limbo's Heart


Magnetism
Defeat Hod


Consistency
Defeat Gheb


Gravity
Defeat Yesod


Radiation
Defear Kether


King Slayer
Kill the Demiurge Ras'Samrah
Found in Ras'Samrah castle after progressing through Niphur

Mercy
Kill the Demiurge Andras
Found in Khotar

Blind Justice
Kill the Demiurge Malkhel
This is the final boss

Did i get something wrong?
Did you find a NPC location i dont have?
Let me know ! :)

My first guide, thought i would give it a try since no one else had made a completion guide for this game yet.
I hope it was helpful.