Moonscars has 34 achievements; some of them are missable and / or mutually exclusive. To get every achievement in the game, you will need to do one full playthrough and one partial playthrough.

To do all achievements in one playthrough, you can backup your save before making some achievement-relevant decisions and restore it after getting the achievements. The save files can be found in AppData\LocalLow\Black Mermaid\Moonscars folder, the game data is stored in Slot1_Rel.json file (the number in the filename corresponds to in-game save slot you're using). I've noted the relevant backup points in the NPC achievements section below. Make sure to disable Steam Cloud saves before replacing your save with a backup one!

Note that most of the achievements have to be completed before reaching the point of no return before the Red Irma fight. (The game tells you where that point is.) If you follow this guide and the map linked below and back up and restore your save to get the mutually exclusive achievements, the only achievements you should be missing when progressing past the point of no return are:

• Cleft Moon
  
• Finale
  
• Farewell, Friend
  
• The Cruel Queen
  
• Moonscarred

These achievements are unlocked as you progress with the main story and cannot be missed.

The First Mould
Cast the very first clayborn mould.


Broken Reflection
Slay the first doppelganger of Irma.
Some mirrors require you to sacrifice your special weapon before you can use them; if you use a mirror like that, Irma is transported back to the Mould Workshop. Teleport back to the mirror that's now marked with red and kill the doppelganger there to get your special back. The first mirror like that is the Upper Slums one in the starting area, you will need to kill the doppelganger there to proceed into the next area.

Traitor's Lot
Slay Traitor Chokran of the Pristines.


Innocence
Slay Gniewko, the Royal Infant.


Lost Friend
Slay Sweet Wanda of the Pristines.


The Last Night
Slay Cruel Lajos of the Pristines.
Note that this achievement is given after you defeat Lajos for the second time.

Cleft Moon
Slay Red Irma and cleave the Moon.


Finale
Complete the story of Grey Irma.

These achievements require specific actions on the player's part. Most of them are difficult to miss and will be obtained while playing the game naturally.

She Craves
Fall under Moonhunger for the first time.
Moonhunger starts if you die when you have five spite bonuses (maximum level). During Moonhunger the moon icon in the top left corner becomes red, the enemies are buffed but give more bone powder.

The Redemption
Alleviate Moonhunger for the first time.
You can alleviate Moonhunger by spending a Gland at a mirror. (Glands can be found in set locations while exploring or rarely dropped by enemies while Moonhunger is active. You can increase the drop rate of glands by spending bone powder at mirrors.) Killing a boss also alleviates Moonhunger.

Try Them All
Discover all Special Weapons.
There are five types of special weapons in the game: Hammer, Harpoon, Painwheel, Spear, and Whirlwind. Every time you defeat a boss or a doppelganger you get to choose a new special; you can also get a new special by spending 3 Glands in the Weapon Rite section at any mirror. All weapons count towards the achievement regardless of the way you obtained them. Note that the special weapons increase in level as you progress through the game; this does not affect the achievement in any way.

Hardened Witch
Learn a witchery of greatest power.
Purchase any witchery from the lowest tier in the tree. These witcheries cost 25,000 bone powder each, you only need to learn one (Doppelganger III, Corpse Reasembly III, or Wormhole III).

Gems Holder
Equip gemstones into all available slots.
Practically unmissable. You can get it in the starting area if you explore thoroughly.

The Spiked End
Throw 25 foes onto spikes.


Bloody Carnage
Kill 5 foes in less than 3 seconds.
A good location to get this achievement is the pit to the left of the elevator near The Nursery mirror. Clear the pit first to open the door to get one of hag's eyes, then rest at the mirror and return to find several spiders there. Gather the spiders around you and kill them off with a strong AoE attack like Stone Pillar witchery or the Whirlwind special.

Gland Trafficker
Spend 10 Ichoral Glands.
Ten Glands isn't many, and it doesn't matter what you spend the Glands on. I got it after bying a gemstone from the Moon Priestess.

Heavy Hand
Stun 50 foes.
Practically unmissable, you will likely get it pretty early in the game.

The Delayed End
Kill 25 foes with status effects.
Use poison from Corrosive Touch or Parasite witcheries.

Hands Off!
Parry 50 attacks.
You get the ability to parry red glow attacks during the tutorial. The mobs in the game are fairly easy to parry, and parries are pretty strong, so I recommend giving it a try.

Mould. Die. Repeat.
Die 10 times (and do not fall into despair).

For the these achievements (and for all the achievements in the section below) I highly recommend the high quality game map made by Demajen, you can get it on their website here[www.demajen.co.uk] or in this google drive folder[drive.google.com].

Ichor, health, and weapon damage are increased by collecting glowing items on the map; they aren't difficult to find if you explore the areas thoroughly.

Slice'N'Dice
Maximize regular weapon damage.


Flow of Ichor
Maximize Ichor Gauge.


Tough Clay
Maximize Health Gauge.


Child's Gifts
Receive all gifts from little Adelinka.

To get all three Adelinka's gifts, you need to collect all Exquisite Earrings and bring it to her. To start the quest for collecting the earrings, first find Adelinka in the castle below The Memorial mirror and get her key, then return to the workshop and open the door in the upper right with the key. Talk to Adelinka there, she will give you a mould that will allow you to see the earrings. Note that the earrings are only visible during Moonhunger (blood moon). Personally I've played through most of the game with Moonhunger active and collected them as I played, but you can also wait until the end of the game when Moonhunger becomes irreversible to collect them.

Once you collect 11 earrings, return to Adelinka to get the Ichor Regeneration Gemstone; she will update the gemstone two times: after you bring her 22 and 44 more earrings. You will need all 77 earrings to get her third reward and the achievement. Make sure to collect and give Adelinka all earrings before proceeding past the point of no return to fight Red Irma.

These achievements require you to complete NPCs' questlines. Some of quest outcomes are mutually exclusive and cannot be completed during one playthough; however, you can backup you save before making certain decisions and restore the backup after getting related achievements.

Inevitable Cruelty
Slay the friendly doppelganger.


Aid from Yourself
Receive help from the spared doppelganger.

The pair of mutually exclusive achievements related to your decision about the rogue mould's fate. She appears after you use the Great Mills mirror in the Depths (the second mirror in the area).

Once you use the mirror and get transported to Mould Workshop, backup your save. Return to the mirror, talk to the friendly doppelganger and choose to kill her to get Inevitable Cruelty.

Restore your backup save, return to the mirror, and choose to spare her this time. (Remember you can get a new special for 3 glands at any mirror if you want since the doppelganger takes it away.) Proceed through the game normally until you meet the mould you've spared atop Castle Apex before the elevator to Red Irma boss fight. Talk to her there to get Aid from Yourself achievement and get her to join you for the first phase of the fight.


Treat The Сat
Help Etalag survive to the finale.
To keep Etalag alive, you need to treat the cat with a Milk Vessel three times at three different mirrors. The mirrors are only unlocked for use and fast travel once you treat Etalag. The order of giving milk is important, making the achievement missable, so make sure to find the milk and give it to the cat when they are near a mirror before progressing to the next area.

• Etalag's Burrow in High Castle. The milk is in the far left end of the same passageway.
  
• Forsaken Valley in Depths (the first mirror you find in the area). The milk is in the upper passage to the right.
  
• Abyssal Warmth in Earth Bowels (the checkpoint between Lajos' Rest and Holy Silence). The milk is in some passageways below the mirror.

If you did everything right, you will meet Etalag near the Presence mirror in Castle Apex. Talk to them to unlock the mirror and get the achievement.


No Place To Hide
Bring Her anger upon hermitess Karina.
Karina is near The Nursery mirror, in the iron cage up the large elevator immediately to the left. The first time you talk to her, she will give you a cookie to bring to Adelinka, do as she says. Visit her after beating each major boss, she will offer to sell you bone cookies. You can buy any cookies you want, it doesn't seem to affect her questline.

Once you kill Cruel Lajos for the second time and Moonhunger becomes irreversible, return and talk to Karina. Go back to rest at the mirror and reload the area (either by going to the workshop and back to the mirror or reloading the game) and return to her again to advance her story. Repeat for about four times until you find her cage destroyed and bloody with Adelinka standing next to it. Talk to Adelinka to get the achievement.


Farewell, Friend
Bid Ion the last farewell.
Ion' mould can be found in the Depths in the area above Wanda's arena, on the path to Earth Bowels and The Nursery. Unlike enemy moulds, his is marked with the three dot NPC symbol on the map. Awaken the mould with Ichor and talk to him, he moves to the workshop. Return to the workshop and find him in the upper left room there. Exhaust all his dialogue until he says "Why was I the last?"; return to the workshop to talk to him after every boss, exhausting his dialogue every time.

Ion will appear in Red Irma's arena after you beat her, talk to him again to make him move back to the workshop. In the workshop Ion will be waiting on the way to the final boss, talk to him one more time to get the achievement.


Joys of Motherhood
Bring to old Horpyna clayborn child.
Voids The Cruel Queen achievement, so be careful!
Horpyna is in the Depths, just past the first Cruel Lajos fight and Lajos' Rest mirror. To complete her questline, you will need to bring her both hag's eyes (left in the pit to the left of The Nursery, right in the Depths before the kind doppelganger mirror), then find the Incomplete Mould in the upper part of Earth Bowels, kill Cruel Lajos for the second time and pay the gargoyles at the kiln 10,000 bone powder to turn the mould into the Newborn Clay. Bring the clay to Horpyna to get the achievement.

Again, completing this questline voids The Cruel Queen, requiring another partial playthrough or backing up and restoring your save. If you want to get both achievements in one playthrough, pick up both eyes and the mould while exploring but ignore Horpyna and Yadwiga's request until you beat Cruel Lajos for the second time (you can talk to them, just make sure not to give any of them the eyes). Backup your save after beating the boss, pay the gargoyles to get the Newborn Clay, and return to Horpyna to give her both the eyes and the clay for the achievement. Exit to menu and restore your save file to continue with The Cruel Queen.


Not The Same
Meet Yarema's mould.
Part of The Cruel Queen questline.
First, find and free Yarema in Castle Outskirts, between the Upper Slums and The Fortress mirrors. Go back to Mould Workshop and talk to Yarema there near the room where the Mould Machine with Irma's body is. Exhaust his dialogue.

Meet Yarema again in the throne room in The Gynaeceum after killing the Royal Infant. Exhaust his dialogue, he will leave.

Speak to Yarema again on the path to The Nursery, then find him in the right section of Earth Bowels after beating Wanda. Exhaust his dialogue, he will die, leaving you with Yarema's Gland.

After the Cruel Lajos fight, talk to the gargoyles at the kiln to bribe them with 10,000 bone powder to throw Yarema's Gland into the kiln. Warp back to the Workshop to find Yarema there, talk to him to get the achievement.


The King's Perspective
Listen to all stories of the mad clayborn.
Part of The Cruel Queen questline.
First, find all four clayborn parts when exploring: left arm in High Castle on the way to the Apex, right arm in Corpse Pits, left leg in the upper left room in Mould Workshop, and right leg between the Depths and The Nursery.

Talk to the king's severed head in The Throne Hall in the castle and reassemble him. Speak with him three times to feed him bone powder and listen to his stories; they cost 5,000, 10,000, and 15,000 each (a total of 30,000 bone powder). You will get the achievement after his third story.

The Cruel Queen
Face Queen Yadwiga after her enthronement.
The longest and most convoluted achievement in the game, this requires you to reach the end of the game after getting both Yarema and Yadwiga to the top of Castle Apex. Make sure to also do Yarema's (Not The Same) and King Drahan's (The King's Perspective) questlines, they are required here.

First you meet Yadwiga in the throne room in The Gynaeceum. Talk to her, she will ask you to kill Gniewko, the area boss. Return to her after beating the boss and exhaust her dialogue until she starts asking for hag's eyes. (Speak to Adelinka and Yarema who are there too. Reload the area if necessary.) Note that giving her the eyes voids another achievement (see Joys of Motherhood in section above for when to backup and restore your save if you want to get them both in one playthrough).

Continue with the game normally, speaking to Yarema every time you meet him for Not The Same and collecting the clayborn parts for the king. Make sure to get Yarema's Gland and throw in the kiln after beating Cruel Lajos (see Not The Same in the section above).

Give Yadwiga the eyes after beating Lajos for the second time, exhaust her dialogue. She will ask you to deal with the king next. Find the king near The Throne Room mirror, reassamble him and listen to his stories as descibed in The King's Perspective section above. After listening to his third story, return to Yadwiga and exhaust her dialogue. Return to the throne room and kill the now hostile king to get the Old King's Head. Return to Yadwiga, give her the head and exhaust her dialogue.

She will ask to bring her brother to the top of the castle next. If you did everything described in Not The Same achievement, Yarema will be in the lower right corner of Castle Apex area. Give him 10,000 bone powder, he will move.

Now make your way to the top of the rightmost tower in Castle Apex, both Yarema and Yadwiga should be there. Exhaust their dialogue.

After beating Red Irma in the apex, return to the tower to find Yarema dead. Talk to him and then to Yadwiga to get her reward and the achievement.

If you followed the guide, you should get the final achievement after beating the final boss. Congrats!
Moonscarred
Unlock all achievements.