Here is the full list of all 57 Psychonauts 2 achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Recover your mental energy with a Dream Fluff
Acquire all Upgrades
Tag all Emotional Baggage
Achieve Rank 100
Find all Figments
Purchase all Pins
Crack all Vaults
Completely fill your Astral Wallet
Scavenge all MISSION CRITICAL PSYCHONAUTS ASSETS
Return to where it all started
Dissolve the Deluge of Grulovia
Frequent Fatherland Follies
Break all 3 Gramaphones in Fatherland Follies
Soothe Lucrecia's Lament
Throw a Judge's gavel back at him
Empty Bob's Bottles
Consume a PSI Pop to restore some mental energy
Peruse Cassie's Collection
Purchase all Otto Shot Filters
Discover the Astralathe
Raid the Tomb of the Sharkophagus
Bowl Strike City
Repair Ford Fractured
Max out your Dream Fluff capacity
Max out your PSI Pop capacity
Complete Lili's Request
Achieve Rank 50
Deliver Cruller's Correspondence
Pyro 3 enemies at once
Complete PSI King's Sensorium
Throw a Regret's anvil at another enemy
Find the real Panic Attack during his Phantom attack
Treat Ford's Follicles
Plate Compton's Cookoff
Tune in to a Stray Thought
Take a photo with the Otto Shot
Complete Gisu's Psychoseismometer Quest
Complete Queepie Quest
Help Dion Setup Aquatodome
Fully upgrade a Badge
Upgrade to the Astral Wallet
Find the Family Camp
Equip 3 Pins at once
Revisit a brain through the Collective Unconscious
Visit the Collective Unconscious
Shut Down the Luctopus
Cool Hollis' Hot Streak
Make a connection in Hollis' Classroom
Achieve Rank 10
Talk to Milla in her Office
Receive your first assignment
Upgrade your first Badge
Equip your first Pin
Combine PSI Cards with a PSI Core at the Otto-Matic
Achieve Rank 2
Navigate Loboto's Labyrinth
TK throw an object to stun an enemy