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