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