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