Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Hear Vernon's Ghost Story.
Witness Maloof's transformation.
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.
Re-brain the Children.
Revisit all brains after completion.
Complete Black Velvetopia.
Find all Golden Helmets.
Earn all Merit Badges.
See yourself through the eyes of many others.
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.
Use the bacon. A lot.
Complete the Punchy Target mini-game.
Give the Coach's speech on the stump.
Read many bulletin board messages.
Discover the secret history of Whispering Rock.
Achieve Rank 60.
Uncover Milla's Secret.
Complete Lungfishopolis.
Buy an item from the Camp Store on Christmas.
Cook and consume two different kinds of roast in one sitting.
Achieve Rank 40.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Achieve Rank 20.
Complete Sasha’s Shooting Gallery.
Complete Basic Braining.