Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Achieve Rank 80.
Achieve Rank 101.
Crack all Vaults.
Gather all Figments.
Give the Coach's speech on the stump.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.
Sort all Emotional Baggage.
Redeem all 16 Scavenger Hunt Items.
Re-brain the Children.
Introduce all Camp Kids to Mr. Pokeylope.
Complete the Punchy Target mini-game.
Hear Vernon's Ghost Story.
See yourself through the eyes of many others.
Spy on Bobby's love life.
Witness Maloof's transformation.
Revisit all brains after completion.
Use the bacon. A lot.
Complete Meat Circus.
Achieve Rank 60.
Complete The Asylum.
Complete Black Velvetopia.
Find all Golden Helmets.
Earn all Merit Badges.
Find Edgar's Secret Garden.
Complete Waterloo World.
Complete Gloria’s Theater.
Achieve Rank 40.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Complete Basic Braining.