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