Here is the full list of all 64 Our Darker Purpose achievements.
Complete all other achievements
Get a ten game win streak
Defeat The Imaginaries with less than 50 move speed remaining
Defeat Better Cordy without hitting it with basic attacks
Complete Hard Mode without using any juice boxes
Complete Hard Mode in under an hour
Defeat Dr. Bloodfather with less than 13 health remaining
Beat the game five times
Complete the game on Hard Mode
Defeat His Natural Defenses after killing 21 spawned enemies
Reach the end of Chapter 4 in under an hour
Defeat a feral cat champion
Defeat A Leafy Oversight after letting him absorb 6 or more spores
Donate 10000 credits to the Guidance Counselor
Collect every single piece of lore
Defeat The Administrators four times
Collect the Broken Mirror and the Trapstem Roses in a single game
Complete a sensitive floor while under the influence of Severity
Reach the end of Chapter 2 without using a vending machine
Reach the end of Chapter 3 without rolling
Defeat The Virtuoso while confused
Please sir - defeat the Cauldron of Yesterdayers before A Second Helping
Complete Chapter 4
Deal over 1000 damage with a basic attack on an enemy
Defeat Regan while holding max juice boxes
Defeat The Friendly Foot Stools without taking damage
Save 80 tokens in a single playthrough
Defeat The Box of Nice Things with four or more presents still alive
Donate 5000 credits to the Guidance Counselor
Defeat an Archivist
Defeat Cyndar's Timekeeper without using a time bubble
Defeat The Winged Overseer with 10 or more small birds still alive
Defeat A Buoyant Double after killing three Frosty Doubles
Defeat The Disciplined King in under 75 seconds
Complete Chapter 3
Defeat The Administrators after spawning 13 extra enemies
Defeat The Brick Pile without letting any slime return
Uncover both Goneril's Mallet and Regan's Lunchbox
Finish off Specialist Fenwick with at least four patients unconscious
Donate 1500 credits to the Guidance Counselor
Defeat Regan three times
Drink 500 Juice Boxes
Heal only a single damage with a juice box
Deal over 400 damage with a basic attack on an enemy
Collect and hold 40 tokens in a single playthrough
Defeat The Obsolete Operator with five or more trash can Broggs still alive
Collect both the Gourmet Turtle and the Wandering Crab in a single game
Donate 100 credits to the Guidance Counselor
Finish off Some Harmless Markings with a chalk cloud
Defeat the Candelabra of Longing without leaving the light
Donate 500 credits to the Guidance Counselor
Complete Chapter 2
Carry ten or more consumables at once
Complete Chapter 1
Meet your demise in Edgewood
Defeat Frothy the Dragon without taking damage
Finish Sudsy the Inanimate with his own glacial spike
Defeat Goneril twice
Meet your demise in Edgewood again and again and again
Collect 35 items over multiple playthroughs
Defeat The Frozen Few without failing a maze once
Defeat Goneril before destroying any buildings
Roll while holding the Fragile Roly Poly and the Candelabra Matchsticks
Defeat 500 enemies in the Edgewood Home for Lost Children