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