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