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