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