Theres only a few unmissable achievements which are tied to regular game progression:

Goblin Tales
Hear all of the Goblin Merchant's tales.
Shortly after defeating Yuri when you activate the Bridge for Boris.

The Fallen
Defeat Sadora the Ascetic.
Simply defeat her shortly after Jun's Bossfight (can be "missed" by never opening a chest)



Theres 3 different Endings to the regular story, one which can only be obtained on Veteran or Hardcore difficulty. These Endings are:

The End
Arrive at the end.
Beat the game by failing the "An Ascetic Lifestyle" Quest and not having the Holy Sword.

Reincarnation
Discover another ending.
Beat the game by completing the "An Ascetic Lifestyle" Quest (dont open any chests before meeting Sadora in the upper castle) and defeat Beatrice with the Holy Sword at the end.

Arrive Home
Arrive at the one true ending.
The same as "Reincarnation" but it needs to be done on Veteran. On Hardcore you get it guaranteed since you get the Holy Sword regardless of opened chests. Thanks to レミリアお嬢様 for pointing out that the achievement DOESN'T pop when done on hardcore.



After beating the game once you'll unlock 3 new gamemodes.
In each gamemode you get a unique Artifact thats changing certain aspects of the Heroine and the enemies. I'll list the artifacts under the achievements. Some pieces of Equipment change their stats inbetween gamemodes as well.
Beat all of them to get those achievements.

Trio
Complete Boss Mode.
In Boss mode you have to switch between Kana, Yuri and Jun who all have different movesets, weapons and abilities at their disposal.

Trinity

• Fire, Ice, Poison and Bleed damage stack
  
• Enemy's critical damage +50%

Witch
Complete Witch Mode.
In Witch mode you're limited to only spells and you cant use any weapons.

Witch Hat

• Maximum HP -40%
  
• Regenerates +1 MP
  
• Regenerates +1 MP while oily
  
• Fire, Ice, Poison and Bleed damage stack

Assassin
Complete Assassin Mode.
In Assassin mode youre limited to only Daggers, Bows, Shields and Wands and you cant use any spells.

Assassin's Greed

• Maximum HP -40%
  
• Critical damage +50%
  
• +1 HP when you land a critical
  
• Fire, Ice, Poison and Bleed damage stack

Hardboiled
Complete Hardcore Mode.
In Hardcore Mode your savefile gets deleted after you die, however, theres 3 Floppy Disk items which work as a 1-Up. The first one is at the Base camp, the second one you get from Sadora after defeating Lami and the last one is in Sadoras Sacred Alcove in the Upper Castle. Manual Saving is disabled, Autosaves only, and no Alt+F4 cheesing either, once you die one Floppy Disk is gone. You can however manually load the last Autosave without penalty. I highly recommend to do a playthrough on Veteran difficulty first and to make seperate saves before each Boss so you can train and come up with strats before tackling them in Hardcore.

Deathly Hallow

• Enemy's attack power +100%
  
• Enemy's critical damage +50%
  
• Save file will be deleted when you die
  
• Fire, Ice, Poison and Bleed damage stack

Quite a few Achievements require you to collect everything of a certain type. i highly recommend this guide by Alisterchadwick who made a detailed Map showing every item and where it can be found. Ill provide some spreadsheets in this guide as well for convenience sake.

Artifact Collector
Collect every artifact.

Art Collector
Collect every art piece.
There are 3 golden tickets hidden in toilet rooms, i marked them with a red square.













I recommend checking out Alisterchadwicks map and guide for the following 7.

Treasure Hunter
Open every treasure chest.


Explorer
Visit every area.


Troubleshooter
Complete every quest.


Librarian
Collect every record.


Spell Master
Collect every Spell.


Weapon Master
Collect every weapon. You need to complete the 'Ascetic Lifestyle' Quest in order to get the Holy Sword, You can however give the Katana to Kana to complete 'Kanas Request' and still get the achievement.


Hoarder
Collect every piece of equipment.

Since the tables are too much for the previous Tab ill put them here. Thanks to Silk for pointing out some Errors in the table.

• Journal #1 - #10
  
• Jun's Journal #1 - #4
  
• Kana's Journal #1 - #2
  
• Lami's Journal #1 - #3
  
• List of Ingredients
  
• Rosie's Journal #1 - #3
  
• Smartphone Message #1 - #7
  
• Yuri's Journal #1 - #3

The biggest chunk of the list are the combat achievements which range from defeating certain enemies to using certain weapons or spells. Ill sort them by type.


Boss Killer
Defeat every boss.
There are 5 main story bosses and 2 optional ones. The optional ones are at the snow planes and the treasury where you encounter Jenny.



To get to this Boss you need to open the Chest labeled as B6. It doesnt count as a regular chest so the "An Ascetic Lifestyle" Quest is not gonna fail.


Inquisitor
Defeat 66 Demon or Undead enemies.
Undead enemies are zombies and skeletons, they can be found in the sewers and catacombs; demons are usually enemies with red or blue skin and can be found at the upper castle.

Bug Hunter
Defeat 60 bugs.
Bugs are small insects like spiders or worms in the sewers or the bow wielding insectoids and big bees in the garden.

Lumberjack
Defeat 30 Plant monsters.
Theres only 3 kinds of plant monsters which are the big poison breathing plant, the screaming girl who digs through the ground and the mushroom. The first 2 can be found in the garden while the mushroom is mainly in the sewers. Thanks to Manas for the information regarding the mushroom!



Orcs Must Die!
Defeat 5 Orcs.


Orcs are the giant green enemies which can be found mainly in the lower castle but also in the garden.









Ghost Buster
Defeat 10 Banshees.


Banshees are the screaming ghosts which can be found in the catacombs.













Using certain Equipment combos make some of these achievements much easier.

Gladiator
Defeat 47 enemies with a Gladius.
The Gladius is the first weapon you'll encounter, get the Leather Gloves and the Gladiator's Armor to make the Gladius really good.

Holy Knight
Defeat 20 enemies with a Holy Sword.
You get the Holy Sword after completing the "An Ascetic Lifestyle" Quest (not opening any chests till after Jun's bossfight)

Marksman
Inflict 50 critical hits with a Bow.
Fastest way is by getting the Multishot Bow by completing the "Astarte's Request" Quest and getting behind a big enemy like an Orc. Use the Rangers Hood for faster Bow attack speed.

Oops
Get your attacks blocked by enemies 50 times.
A quick way of getting this is by using the summon sword spell from the "Beatrice's Request" Quest and using it in front of a big plant enemy.

Roughneck
Defeat 50 enemies with a Sledgehammer.
The Sledgehammer is a very slow weapon so the timing can be a bit tricky. Use the Gauntlets and the Goblin Shamans Mask and defeat some goblins in the Lower Castle.

Shield Crusher
Land 50 attacks on enemies by penetrating their shields.
Look for weapons that have the *ignores defense* tag and use those on either skeletons with shields or the big plants. I found the throwing meat from Rosie the easiest.

Sling of David
Inflict 30 critical hits with Throwing weapons.
The throwing meat works the best for this one as well.

Trap Master
Defeat 20 enemies by using traps.
Traps can be any environmental contraptions like fireball canons, shocktraps or lightning lasers. Theres a good spot in the upper castle to farm these kills. Kills inflicted with poisoned water also counts toward this achievement. Thanks to Matinny for the info!

Sword Master
Deflect 20 enemy attacks with a Katana.
The katana is a Quest item and cant be gotten back once you hand it over to Kana. You can avoid her by jumping down the elevator shaft after getting it. Fastest way of getting it is to get in front of a Goblin Totem and hit its fireballs. Use the Gauntlets for faster attack speed.



Cryomancer
Defeat 50 enemies with ice spells.
I recommend doing this one at the same time as the Rune Master achievement since frost runes are pretty good for both. Get the Ice Cream Scoop, the Mages Orb and the Rune Stone to get the most out of your Ice Runes.

Necromancer
Defeat 44 enemies with Corpse Absorption spells.
The corpse absorption spell can be found in the same room as the optional chest boss. Using the spell on zombies and skeletons damages them so you can use it in the catacombs a lot. Get the Saints Skull and the Mages Orb to get the job done.

Pyromancer
Defeat 50 enemies with Fire spells.
Theres quite a few good fire spells, the best one in my opinion is the "summon fire orb" spell in combination with the magic amulet item.

Rune Master
Defeat 30 enemies with Runic spells.
Use the Magic Orb and the Rune Stone to make any Runes pretty good.

The remaining achievements wich require different tasks.


Meat Lover
Consume 100 Meat items.
You can save scum this one by getting a few meat items (roasted chicken, ham, barbecue), saving and reloading after eating all the items you have. Repeat this until you get it.

Money Swag
Earn 999 gold.
You can also safe scum this. Safe before a vendor and sell all the items you have till you get past 999 gold. Reload so you dont lose your items.

Iconoclasm
Destroy 5 icons.
Icons are the statues of the boyband in the catacombs. Ive marked the locations on the map ranging from O1 to O5


Icon 1


Icon 2


Icon 3


Icon 4


Icon 5