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