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