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