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