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