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