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